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A THEORY 



OF 



Gravitation, Heat and Electricity 



1 ^j 



BY MELTILLE MARBURT. 






■ j:i 23 1881 41 



BALTIMORE: 

No. 174 West Baltimore Street. 
1881. 



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Copyright, Melville Marbury, 1881. 



I^ress of John B. Fiet^ Baltimore, 

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ooisrTEi<rTS. 



Chapter. Page. 
/. — On the Nature of the Gramtaiing Force 1 

II. — The Forces of Gravitation^ Cohesion and Chemical Attraction 
are due to a Peculiar State of the Interstellar Medium, 
which is Composed of two Ethers of Unequal Elasticity, one 
of ichich Pervades and has the Power of Compressing the 
other 15 

III — Heat ; or, tlie Bepulsite Forces of Matter due to a Rotatory 
Motion of Atoms and Molecules, and to tlie Effect of such 
Motion upon the Interstellar Medium 30 

IV. — On Radiant Heat and Light J^G 

V. — Electricity Explained on the Double EtJier Hypothesis^ the 

Basis of the Preceding Theory of Gravity and Heat 62 

YL — On Magnetism 83 

yil — On the GcTieral Disturhance of Ekctriccd Equilibrium by the 

Movements of the Heavenly Bodies... 91 



A THEORY 



OF 



Gravitation, Heat and Electricity 



OHAPTEK I. 

ON THE NATURE OF THE GRAVITATING FORCE. 

There are two principal forces of matter, one which draws 
or impells, the other tending to separate bodies. In the 
present treatise, that force which impells bodies is supposed 
to be seated in the interstellar medium; the separating force 
is inherent in the properties of the bodies themselves which 
are acted on. In order to explain them, we must have not 
only a theory of the properties of bodies on which they act, 
but we must have a theory, too, of the nature and constitu- 
tion of the interstellar medium. It is a theory of this 
nature that I propose to develop in the following pages, 
beginning at chapter second. According to my view, 
gravity proceeds from the pressure of the interstellar 
medium, and is not the attraction of matter ; heat and the 
other repulsive forces depend on the motions of molecules 
and atoms, but the particles of matter act not immediately 
upon one another, but through the interstellar medium. 
All this I will explain in the proper place, and will embrace 
in the same general theory an account of the phenomena of 



)i A THEORY OF GRAVITATION, 

gravity, affinity, heat, light, electricity and magnetism, and 
will show the relations of these forces to one another. But 
before proceeding with this, I will advance a few arguments 
to combat the common idea of attraction, and will devote 
the first chapter of this treatise mainly to that purpose. 
Some of these arguments are not new, but while the common 
idea of gravity prevails, a new theory of this force could not 
be properly introduced without them. 

I am not sure that everyone will agree with me through- 
out as to the nature of force in general, though all of us, I 
think, must start together. Our first conceptions of force 
are derived from the inertia of bodies, either when we 
attempt to set them in motion, or when, being already in 
motion, we attempt to arrest them ; in other words, it is that 
idea of force which is derived from mechanical action. But 
when we attain to more experience, and perceive that 
mechanical action may be produced by gravity, heat or 
electricity, and that these in turn, with exception of gravity, 
may be produced by mechanical action, we have come to 
apply the term force also to these agents. We find also that 
these forces are commeasurable, and that a definite amount 
of one is consumed or disappears in producing its equivalent 
of another. When this occurs, we do not say that one is 
annihilated, and that another to take its place is created, 
although, for all we know to the contrary, this may be the 
truth of the case ; but we assume, upon the strength of a 
certain faith which we have in the immutableness of the 
Divine Nature, which is the true basis of the doctrine of 
conservation, that no creation and annihilation occurs, but 
that the forces are converted, and when mechanical action 
produces heat, it does not create heat, but becomes heat, and 
the motion of masses becomes the motion of particles. 

The doctrine of the conservation and convertibility of 
forces has been established by experiment in reference to all 



HEAT AND ELECTKICITY. 6 

of the forces, which I have enumerated, except gravity, 
which alone has defied it, for while examples occur of its 
producing the other forces, none occurs in which it is pro- 
duced by them, and instead of losing, as the others do, by 
production, it appears to gain in strength at the same time. 
But where these forces are convertible one into another, they 
must be all of the same nature. For, to convert dissimilar 
natures one into another, is an act of creation. It implies 
even more than this — a two-fold exertion of infinite power — 
both annihilation and creation. For who can conceive the 
conversion of matter into mind? or, rather, who does not 
perceive that it implies a contradiction ? And why is this? 
It is because their natures widely ditier. In like manner, no 
two things can be convertible without creation, it matters not 
how near their natures approach in kind, unless they be 
identical. Conversion can only apply to the different condi- 
tions and phases of the same thing. Consider, for example, 
the truly essential properties of matter, as extension, form, 
impenetrability, mobility and inertia. Kone of these prop- 
erties are convertible. Their natures are entirely unlike, 
and their convertibility is impossible. But the forces of 
matter are concerned alone Avith the properties of its 
mobility and inertia. None of these properties can produce 
force^ but force is rather a condition of these properties. 
Properties are unalterable. They can neither change nor be 
changed without creation, nor produce anything but them- 
selves. Therefore, I propose to argue that the cause of 
gravity is not a property of the body that gravitates, but a 
force or condition, depending on a peculiar constitution of 
the interstellar medium. But first let me endeavor to illus- 
trate what is meant by force, which is consumed or con- 
verted, and is capable of being measured. Let us, then, 
suppose a mass to be freely suspended in the air, and that 
we exert our strength against it and set it in motion. If we 



A THEORY OF GRAVITATION, 



now oppose the motion,, which the body has thus acquired, 
we shall have to exert as much strength to stop it as we 
exerted at first to produce the motion. Now the question 
arises, whether the expenditure of our strength has imparted 
anything to the mass which it. did not possess before? I 
answer: Ko, but the same space-appropriating power of the 
matter acts without increase or diminution, whether the 
body is at rest or in motion ; but, in being changed from 
motion to rest, or from rest to motion, the direction of its 
action is changed. This change or conversion takes place 
within the suspended mass, and does not pass from one body 
of matter to another. It may be allowable, for convenience 
of expression and in conformity with usage, to say that force, 
meaning ino^nenhiin or resistance^ passes from one body to 
another in contact; but the expression should not lead us to 
regard force as a being or creation in the same sense as 
matter or mind. It is simply a condition. But it just as 
much requires a cause to change it. This cause, which 
changes the condition of motion or rest of one body, may be 
a condition of the opposite nature in another body. Thus 
in the case of a moving body, A, colliding with another 
body, B, at rest, the condition of the one is the force which 
is expended in producing a change in the condition of the 
other. The amount of dissimilarity of these two conditions 
is what constitutes the intensity of the force. The amount 
of momentum, depending on the amount of matter involved, 
constitutes the strength of the force. This is a simple illus- 
tration of force, which may be defined in general terms as a 
cause of a physical action, Avhich is itself changed in 
producing change. 

Now the question is, how we are to include gravity in this 
definition of force, since it appears not to be converted or 
consumed, like other forces, in producing change. Mayer, 
the eminent advocate of the doctrine of the conservation 



HEAT AND ELECTRICITY. 5 

and correlation of forces, attempted to relieve himself of the 
difficulty of this question by the assumption, that gravity — 
since it is not changed in producing change — is a property 
of matter, and not a force. But Faraday, carrying the con- 
servation principle still farther, embraces gravity also in his 
idea of force; and because it is the cause of a physical 
action, inferred that the cause of gravity must be consumed, 
although the exact nature of the change has not yet been 
ascertained. ^' There is," says he, ^'one wonderful condition 
of matter, perhaps its only true indication, namely inertia; 
but in relation to the ordinary definition of gravity it only 
adds to the difficulty; for if we consider two particles of 
matter apart, attracting each other under the power of 
gravity and free to approach, they will approach, and when 
at only half the distance each will have stored up in it, 
because of its inertia, a certain amount of mechanical force. 
This must be due to the force exerted, and if the conserva- 
tion principle be true, must have consumed an equivalent 
proportion of the cause of gravity." 

Formerly there were considered to be many forces distinct 
and dissimilar in their nature, such as could produce change 
without being changed themselves. But now it is alleged 
that the effect is produced by conversion. When electricity 
produces heat, it is converted into heat; and when heat pro- 
duces electricity, it is converted into electricity. But if 
recent investigations have demonstrated the conservation 
and the convertibility of all these causes of physical action, 
the opinion that these forces are dissimilar in nature can no 
longer be entertained; for to convert dissimilar natures one 
into another is as much an act of creation as to originate 
them. For, on what principle do we rely for the proof that 
heat is a mode of motion ? Is it not the fact of the con- 
version of mechanical force into heat and the principle 
derived from reflection that only things of the same natura 
1* 



A THEORY OF GRAVITATION, 



are convertible'? If this principle is not true, heat is not yet 
proyed to be a mode of motion, but may be a repulsive 
property only of the opposite nature to attraction, and the 
particles of matter may repel as well as attract through a 
vacuum. Without this principle we cannot prove that heat 
is a force and not a fluid. But holding the principle to be 
true, we conclude that heat, into which mechanical force is 
converted, is the same nature under another form; that the 
motion of masses is converted into the motion of their par- 
ticles; and that as masses rebound when they strike 
together, so the collision of the invisible particles of matter 
produce repulsion and the phenomena of heat. The same 
reason applies to electricity, to magnetism, and to gravity, 
which must therefore like heat be of the same nature as 
mechanical force, conditions of matter, and not properties 
of matter. It is true it has never been shown that any of 
these forces are converted into gravity, but gravity may be 
made to produce these forces ; for gravity produces mechan- 
ical force and mechanical force may be converted, by impact 
or friction, into heat or electricity, while chemical affinity — 
which is attraction between the particles of matter — is the 
chief terrestrial source from which these forces are developed. 
To show that the ordinary definition of gravity as a 
property of matter implies a departure from the principle of 
the conservation offeree, we may take an illustration of this 
subject from the action of gravity upon the motions of the 
celestial bodies, by which action is apparently produced a 
creation and an annihilation of mechanical forces. The 
Earth, for example, moves in its elliptic orbit with more 
velocity at one season of ihe year than at another. Its 
motion is quickened as it approaches the Sun, and retarded 
as it recedes. Unless, then, its motion is in some way 
converted, it is lost. We cannot suppose that the Earth 
parts with motion into a vacuum, or that it receives motion 



HEAT AND ELECTRICITY. 7 

from a yacuiim. If this Avere possible, there could be no 
reliable proof of the principle of conservation, which implies 
the inseparable nature of matter and force. It is true that 
we say the Earth's increasing velocity, as it approaches the 
Sun, is due to gravity; and that its loss of velocity, as it 
recedes, is also due to gravity. Is it possible, then, for us to 
conceive that the mechanical force is derived from a prop- 
erty when the Earth's orbital motion is accelerated, and that 
the mechanical force is annihilated by the property or 
reconverted into the property, when the Earth's velocity is 
diminished, a condition and a property convertible? From 
which reasoning it appears to me that the cause of gravity, 
like the causes of all other physical actions, must be a 
condition of matter and not a property. We must infer that 
gravity is due to a reaction of the same nature as that which 
awhile ago we supposed to take place between the moving 
body and the body at rest, the condition of one body pro- 
ducing a change in the condition of another. We cannot 
otherwise explain the force in harmony with the law of 
inertia and the principle of conservation. A body, to move 
itself, must alter its condition and create a new condition; 
to move another body, it must change the condition of this 
body. It is contrary to daily experience, where the cause 
and effect are such as to come under observation, that this 
change of condition ever occurs in the first case; nor does 
this disturbance of equilibrium ever happen in the second 
case except by reaction or conversion, when the two bodies 
are in contact. Upon this experience we found the doctrine 
of conservation and correlation of forces. Gravity alone 
appears to contradict the principle, and we can remove the 
difficulty, it seems to me, only by the supposition that 
gravity is caused by force or pressure operating through the 
interstellar medium. For then the Earth would part with 
its force or motion into this ethereal matter, when it moves 



8 A THEORY OF GRAVITATION, 

against the pressure of this matter, and would receive force 
or motion from it when moving in the same direction as the 
pressure. 

Certainly, if matter be an involuntary agent, no change 
can take place in its conditiou without external cause, 
material or immaterial. How a material cause may operate 
in producing this change from rest to motion and from 
motion to rest in masses, whose motions come under imme- 
diate observation as in the case of the two colliding bodies 
above mentioned, is readily explained in harmony with well- 
established natural laws of matter. But the production of 
motion by a property or an immaterial agent, as the cause 
of gravity is sometimes assumed to be, since we cannot sup- 
pose that motion can be transferred from an immaterial in 
the same manner as from a material agent, is a different 
thing from convertibility, and implies creation and annihila- 
tion, as Faraday in the following passage clearly demon- 
strates: ^^The idea of gravity appears to me to ignore 
entirely the principle of the conservation of force, and by 
the terms of its definition, if taken in an absolute sense, 
^varying inversely as the square of the distance,' to be in 
direct opposition to it; and it becomes my duty now to point 
out where this contradiction occurs, and to use it in illustra- 
tion of the principle of conservation. Assume two particles 
of matter, A and B, in free space, and a force in each or in 
both by which they gravitate towards each other, the force 
being unalterable for an unchanging distance, but varying 
inversely as the square of the distance when the latter 
varies. Then at the distance of ten the force may be esti- 
mated as one, while at the distance of one— that is one-tenth 
of the former — the force will be one hundred. But from 
whence can this enormous increase of power come ? If we 
say that it is the character of this force, and content our- 
selves with that as a sufficient answer, then it appears to me 



HEAT AND ELECTRICITY. 9 

we admit a creation of power, and that to an enormous 
amount; yet by a change of condition, so small and simple 
as to fail in leading the least instructed mind to think that 
it can be a sufficient cause, we should admit a result, which 
would equal the highest act our minds can appreciate of the 
working of infinite power upon matter ; we should let loose 
the highest law in physical science which our faculties per- 
mit us to perceive, namely: the conservation of force. 
Suppose the two particles A and B removed back to the 
greater distance of ten, then the force of attraction would 
be only a hundredth part of that they previously possessed. 
This, according to the statement that the force varies 
inversely as the square of the distance, would double the 
strangeness of the above results ; it would be an annihilation 
of force, an effect equal in its infinity and its consequences 
with creation, and only within the power of him who has 
created." 

" The usual idea of the force," says Faraday in another 
passage of gravity, " implies direct action at a distance. 
And such a view appears to present little difficulty, except 
to Newton and a few, including myself, who in that respect 
may be of like mind with him. Some are much surprised 
that I should, as they think, venture to oppose the conclu- 
sions of Newton; but here there is a mistake. I do not 
oppose Newton on any point ; it is rather those who sustain 
the idea of action at a distance that contradict him. Doubt- 
ful as I ought to be of myself, I am certainly very glad to 
feel that my convictions are in accordance with his conclu- 
sions ; at the same time, those who occupy themselves with 
such matters ought not to depend altogether upon authority, 
but should find reason within themselves, after careful 
thought and consideration, to use and abide by their own 
judgment.'' The opinion of Newton to which Faraday here 
alludes is found in the following extract : '' That gravity," 



10 A THEORY OF GRAVITATION, 

says Newton, '^ should be innate, inherent, and essential to 
matter, so that one body may act upon another at a distance 
through a vacuum without the mediation of anything else, 
by and through which their action and force maybe con- 
veyed from one to another, is to me so great an absurdity 
that I believe no man, who has in philosophical matters a 
competent faculty of thinking, can ever fall into it. Gravity 
must be caused by an agent acting constantly according to 
certain laws; but whether this agent be material or imma- 
terial I have left to the consideration of my reader.^' Euler 
after Newton, and Descartes before him, reasoned Of gravity 
in the same strain. Kepler accounted for the tides by the 
attraction of the Moon. But Descartes rejected this 
hypothesis; "For to conceive this,^' says Descartes, "we 
must not only suppose that every portion of matter in the 
Universe is annimated and annimated by different souls 
which do not obstruct one another, but that these souls are 
intelligent and even divine, that they may know what is 
going on in the most remote places without any messenger 
to give them notice, and that they may exert their powers 
there.'' The law of gravitation none disputed. It was 
plain, therefore, that bodies are either attracted or impelled 
according to this law. A number of hypothesis therefore 
have been proposed, based on the principle of impulsion by 
thie interstellar medium. One of these by Descartes, based 
on the hypothesis of two ethers, was intended to explain the 
circular motions of the heavenly bodies; another by Newton 
based on the hypothesis of a single fluid of varying density, 
and a third by Le Sage, Avere intended to account for the 
tendency of bodies to approach one another on the theory of 
impulsion. The anxiety of these philosophers to find a 
better explanation of gravity than what is generally 
received, and the favor with which their attempts have been 
viewed by other kindred spirits, are proofs of the difficulties 



HEAT AND ELECTRICITY. 11 

which have been always experienced by those who think 
upon this subject in reconciling the properties of attraction 
and inertia. 

Before the law of universal gravitation was fully 
expounded, the upward motion of flame was thought to 
proceed from a principle of levity. So now it may be that 
our ignorance as to the nature of the reaction of the inter- 
stellar medium upon bodies may lead us to attribute the fall 
of bodies to a principle of attraction. It is the reaction of 
the atmosphere upon the heated gas of the flame that causes 
it to ascend; and why may not a similar reaction of the 
interstellar medium upon bodies produce changes in their 
positions? It might be answered to this that such a 
hypothesis demands too great a result from the action of a 
fluid so rare and subtile as the luminiferous ether. We 
move so easily through space and observe the motions of the 
heavenly bodies so unchanging and unobstructed, that both 
our bodily feelings and our mental deductions might incline 
us to the doctrine of a vacuum. But this objection may 
proceed altogether from an illusion. For we know that the 
atmosphere exerts a pressure of fifteen pounds on every 
square inch of surface, and that notwithstanding this great 
pressure we move freely and without sensible impediment 
from this circumambient fluid. This freedom we attribute 
to its elasticity. The same argument applies to the luminif- 
erous ether. It matters not how great its density or pres- 
sure, if its elasticity is correspondingly great so as to over- 
come the inertia of its particles, it would present no 
impediment or obstruction to the motion of the heavenly 
bodies, nor would we be sensible of its presence. Moreover, 
this objection, which might be raised against an impulsion 
theory of gravitation, applies equally to the undulatory 
theory of light and heat, as any one may observe who 
examines this question. For accepting the undulatory 



12 A THEORY OF GRAVITATION, 

theory of light as an established principle, the pressure or 
^^ bursting power '' of the luminiferons ether, according to 
the estimate of Sir John Herschel, must be about seventeen 
trillion pounds to the square inch, estimating that of the 
atmosphere as fifteen. '*' Do what we will," says he, " adopt 
what hypothesis we please, there is no escape, m dealing 
with the phenomena of light, from these gigantic numbers, 
or from the conception of enormous physical force in per- 
petual exertion at every point through all the immensity of 
space.'' Now, the atmosphere surrounding bodies in contact 
is capable of holding them together by its pressure with the 
force, which I have already mentioned. When we read, 
then, the immense numbers expressing the bursting or com- 
pressive power of the luminiferous ether, need we look 
elsewhere for a force by which the particles of matter are 
held in cohesion whenever they come in contact? We 
rather wonder by what force atoms in contact escape again 
from this gigantic embrace ! 

How this ether produces attraction between bodies not in 
contact, is a question, whicli involves a theory of its constitu- 
tion. The supposition of the existence of such a fluid, which 
Huyghens introduced as the basis of his undulatory theory 
of light, and which Newton suggested might produce by 
impulsion the gravitating force, was previously proposed 
by Descartes as well to explain the properties of light as to 
account for the motions of the planets around the Sun. 
Newton and Huyghens conceived the ether as a single fluid, 
whereas Descartes asserted there were two. Subsequently 
the hypothesis of two fluids was independently proposed by 
Du Fay to explain the phenomena of vitreous and resinous 
electricity, but again fell into disfavor when Franklin sug- 
gested that the phenomena were explainable on the hypothesis 
of a single fluid, and substituted the terms 2J0sitive and 
Qiegative. By a course of reasoning entirely independent, I 



HEAT AND ELECTRICITY. 13 

have come to the same conclusion with Descartes and Dii 
Fay. But in the use to be made of the hypothesis, I shall 
exceed the limits to which it has been hitherto carried. For 
whereas it has been proposed with a view only to a single 
result, that of generalizing facts either under the head of 
heat, or light, or electricity, or gravity, I hope to carry the 
generalization a step farther, and to show that the scope of a 
Double Ether Hypothesis, which it is the object of this 
treatise to revive for a third time, is wide enough to embrace 
in one theory an explanation of gravity, heat and electricity 
in conformity with the doctrine of conservation and con- 
vertibility of forces. Descartes, says Hallam, was driven to 
this hypothesis of a double ether by his aversion to admit 
any vacuum in nature. His reason may appear somewhat 
obscure to us, but is certainly entitled to our respect, not 
simply out of consideration for the genius of its author, but 
from the fact that from the same idea of the immutability 
and divine perfection of the Creator, Descartes deduced 
another important principle, that there must always be the 
same amount of motion in the universe, and that no motion 
can be lost, which I understand to be the same thing, as is 
referred to in modern philosophy as the conservation of 
force. But whether his reason be received or not, it is 
certainly just as easy to suppose two fluids as one, or to sup- 
pose even three or more, if necessary to explain natural 
phenomena. For it is not supposed that they occupy the 
same space, but that one pervades the pores of the other. 
The atmosphere itself is not a single fluid, but composed of 
many; and what is more remarkable, each one of the gases 
or vapors which compose it exerts its own separate, individ- 
ual pressure. In like manner, I suppose that space is filled 
with two ethers, and that each exerts its own separate 
pressure. 

The suppositon that ether is endowed with an expansive 



14 A THEORY OF GRAVITATION, 

elastic property seems to require one of two hypothesis: 
either, as Sir John Herschel says, that the universe may be 
surrounded with a hard or crystalline shell capable of con- 
fining and resisting the outward pressure of the ether, and 
preventing its expansion ; or else that there is a continual 
production of new ether at the centre of the universe, so as 
to fill the vacuum caused by its expansion. It seems to be a 
law of nature that nothing is wasted. The old and effete 
matter of worn out worlds becoming useless, when it has 
reached the centre of the universe, may be there converted 
by the Almighty into imponderable matter, and this may by 
the law of its nature have an outward tendency, just as all 
ponderable matter has a tendency inwards. On the other 
hand, the ether, when by expansion it has reached the con- 
fines of our universe, must become useless as ether, and may 
be there converted into ponderable matter, and precipitated 
back into the universe again on an inw^ard mission of Provi- 
dence. This work may not necessarily be regarded as a 
creation of something new, but a separation and combining 
again of the primary elements of matter. These specula- 
tions, which are the legitimate fruit of the hypothesis of an 
elastic medium, are beyond the province of demonstration 
or proof, but appertain to the undulatory theory of light — 
which is now commonly received — no less than to an impul- 
sion theory of gravity. 



HEAT AND ELECTRICITY. 15 



CHAPTER JI. 

THE FOKCES OF GRAVITATION, COHESION AND CHEMICAL ATTRACTION 

ARE DUE TO A PECULIAR STATE OF THE INTERSTELLAR 

MEDIUM, WHICH IS COMPOSED OF TWO ETHERS 

OF UNEQUAL ELASTICITY, ONE OF WHICH 

PERYADES AND HAS THE POWER OF 

COMPRESSING THE OTHER. 

The processes of Nature are connected by a series of 
analogies, by means of which we not only trace a unity of 
design and workmanship in the whole, but ascend step by 
step to a more thorough knowledge of the physical world. 
The modern theories of sound and light and heat are 
derived from these anologies, and it is upon the strength of 
conviction which they are calculated to enforce, that I have 
been encouraged to undertake a theory of gravity, in which 
the principle of impulsion is substituted for that of attrac- 
tion at a distance. All the other forces of matter have been 
explained in accordance with the doctrine of conservation. 
This must be explained in harmony with the same principle, 
if it is analogous to the rest. Experience rejects the idea 
that matter can act, where it is not or has no channel of 
communication. We could not be satisfied that sound could 
pass from a distant object to us, unless matter were the 
channel through which, or by means of which, it is con- 
veyed. Either then it was an emanation from the sounding 
body, which was readily confuted, or it was an undulatory 
motion through the atmosphere like that which is seen on 
the surface of water, when its molecules are subjected to a 
sudden displacement Secondly, light, for the same reason 
as sound, required a medium, and this medium, like that of 
sound, must be a material medium ; it must consist of par- 



16 A THEORY OF GRAVITATION, 

tides emitted from the luminous body; or it passes like 
sound, by the undulation of an elastic fluid. The air was 
found to be too coarse a substance for the enormous velocity 
of light, and ether was invented; hence arose the undulatory 
theory of light. 

Reasoning from the very same principles, men have tried 
to explain gravity, which requires, as well as sound or light, 
the existence of some medium between the distant objects 
between which it acts. The very same agent which produces 
light has been suspected, but the mode of its action has not 
been explained. The nearest approach to an explanation 
is the hypothesis of Sir Isaac Newton, "that all bodies are sur- 
rounded by an elastic fluid, which increases in density 
outwardly from the bodies which it surrounds; and that 
gravitation is the tendency of bodies to pass from the denser 
parts of this fluid to those parts where it is rarer; and that 
in this way bodies are impelled to one another.'' This 
hypothesis labors under one difficulty, that of explaining 
how the elastic fluid is kept in such a condition of varying 
density as here supposed. It is for the removal of this 
difficulty, and not for the substitution of a new theory, that 
I have invented the hypothesis of a second fluid, less elastic 
than the ether, and pervaded by it. The theory itself, like 
the undulatory theory of light, is supported by an analogy 
to the action of air; and as the one may be derived from a 
knowledge of the air's motions, so the other from its 
pressure. 

It is said that air exerts a pressure of fifteen pounds' to 
the square inch on all bodies at the surface of the Earth. 
If, therefore, the surfaces of two bodies be brought in contact, 
the pressure of the atmosphere on their farther sides will 
cause a cohesion between the bodies, which will require 
a force, for every square inch of surface in contact, equal to 
raising fifteen pounds to separate them. Here, then, is a 



HEAT AND ELECTRICITY. 17 

species of cohesion produced between common or sensible 
matter by the pressure of an elastic fluid, the air, surround- 
ing the Earth. The force which holds the two masses 
together is in the atmosphere, and is not a property of the 
masses. Likewise, the force which is employed to separate 
them is exerted against the body of the atmosphere and not 
against the masses. We see similar effects between the 
minute particles of matter; but we know that the air is not 
of sufficient tenuity to pervade the pores of bodies, and to 
produce these effects upon their minute particles; and 
besides this the molecular forces are much more intense than 
the pressure which is produced by the atmosphere. Hence, 
in order to account for the cohesion between atoms and mole- 
cules of matter, we have to suppose the existence of a fluid 
more subtile than the air, and at the same time more elastic. 
The investigation of the phenomena of light has proved the 
existence of such a fluid ; but this does not afford us a full 
or an exact explanation of cohesion or gravity. For that 
bodies which gravitate are not in contact like those bodies 
which the air holds together by its pressure is evident to all, 
and we know too from closer study that atoms and molecules 
are not in contact; and, moreover, I shall attempt in the 
course of this theory to prove that they never come into con- 
tact. What we have said, however, may be regarded as a 
coarse illustration of the manner in which a fluid may pro- 
duce by pressure a certain kind of attraction ; and the 
analogy of this action of the atmosphere to the aclion of 
cohesion between the particles of matter — taken together 
with the proof from light of the existence of the ether, with 
its all-pervading and elastic pi^operties — is strong enough to 
encourage us to base much upon it, and to pursue the resem- 
blance as far as any exists. The elastic force of the atmos- 
phere at the surface of the Earth is due in great part to its 
gravity; and the elastic force of the medium, which we 



18 A THEOKY OF GKAVITATIOlS-y 

suppose to act upon the minute particles, must likewise be 
due to some sort of compressive force. But how the 
Almighty effects this compression it is needless to inquire, 
as it is impossible to determine : it is enough for our purpose 
that, if there be any interstellar medium or ether, as com- 
monly supposed, of that nature which is described in the 
undulatory theory of light and radiant heat, the known 
properties of matter lead us to conclude, that, without heat, 
it would produce some sort of cohesion, in the same manner 
as air, between loose particles of matter in contact. By loose 
particles I mean such as have no forces of repulsion or 
attraction acting upon them. Let us then follow out this 
idea of impulsion suggested by the pressure of the air. 

The luminiferous ether is commonly represented as a 
single fluid, and so far w^e have only considered it as such. 
But two philosophers, Descartes, in his account of light and 
gravitation, and Du Fay, in his theory of resinous and vitre- 
ous electricity, have presented the idea of two fluids. I 
have already suggested my reason for adopting a hypothesis 
of a double ether, and I will now proceed to point out more 
fully what I conceive to be its nature, and the relations of 
the two fluids composing it. Some idea of this may be gotten 
from the following extract from the writings of Descartes; 
but I will give the two fluids names, and for the purpose of 
distinction will call the more rarefied ether, and the other 
caloric: "1 will tell you," says Descartes, in a letter 
addressed to a friend, ^'that I can conceive, or rather can 
demonstrate, that besides the matter which composes terres- 
trial bodies, there are two other kinds, one very subtile, of 
which the parts are round like grains of sand, and this not 
only occupies the pores of terrestrial bodies, but constitutes 
the substance of all the heavens; the other incomparably 
more subtile, the parts of which are so small and move with 
such velocity that they have no determinate figure, but 



HEAT AND ELECTEICITY. - 19 

readily take at every instant that which is requisite to fill all 
the little intervals which the other does not occupy.'^ 

The etlier and caloric, for so we have named the two fluids, 
either separate or combined, pervading all other matter, 
might produce, in the absence of heat, that sort of cohesion 
between molecules which we have already pointed out. la 
the same manner we may suppose that ether pervading the 
pores of caloric with the utmost freedom, Avould produce 
cohesion between its atoms when brought in contact, pro- 
vided the pressure of the ether were sufficiently great to 
arrest the motion of the caloric particles. It is plain that 
the pressure of the etlier, would in this way diminish the 
elasticity of the caloric, and that the caloric, therefore, 
would be a less elastic fluid than the ether. For while the 
ether would diminish the elasticity of the caloric, the caloric 
could have no such corresponding effect upon the elasticity 
of ether, for here the analogy is perfect between the pressure 
of the ether upon the caloric particles and the pressure of 
the atmosphere upon bodies, which it may be made to hold 
in contact. As the air is not afi'ected in its elasticity or 
expansive force by the presence of these bodies, neither 
would the ether be affected or lessened in its elasticity by 
the presence of the caloric particles. The expansive force 
or elasticity of caloric, therefore, cannot be infinite, and as 
compared with ether, there may be considered to exist a 
slight cohesion between its particles. 

I have now given a reason for the supposed difference of 
these two fluids in respect to elasticity, namely, the reaction 
of one on the other. I am now to explain how that pressure, 
which can produce the cohesion of bodies in contact, may be 
so modified as to produce the approach of bodies not in con- 
tact ; the force of gravity being the residue of that pressure 
which the ether exerts in compressing the caloric. We have 
supposed all space to be filled with at least three species of 



20 A THEORY OF GRAVITATION, 

matter. First, at the center of the universe is a solid mass 
of what, under the influence of ether and caloric, is ponder- 
able matter, composed of atoms comparatively speaking very 
large. Second, above this and around it is an atmosphere of 
caloric, varying and decreasing in density as it extends 
outwardly, and composed of atoms very much smaller than 
the first. Third is the ether, which fills the pores of the 
two other species of matter. It increases in density as the 
caloric diminishes, the two fluids being thus oppositely 
arranged and together filling space. The ether's condition 
is therefore like that of the fluid m the hypothesis of Sir 
Isaac Newton, in which he suggests that there is an elastic 
medium pervading all space and increasing in density as we 
proceed from dense bodies outwards, that this '•'causes the 
gravity of such dense bodies to each other, every body 
endeavoring to go from the denser parts of the medium to 
the rarer." 

It is plain that the condition of the ether, since it freely 
occupies all space, is due to the presence within it of the two 
other species of matter. But we suppose the main cause of 
the varying density of the caloric to be the circumambient 
and pervading ether, acting by pressure both upon the cir- 
cumference of the caloric from without, and also inwardly 
upon the caloric atoms, and retarding their expansion. 
(But it might be that the caloric reacting upon itself in 
expanding would produce the same result.) We are to 
consider that the ether exists not only within the caloric, but 
that it extends much beyond it, and environs it just as the 
caloric environs the dense body at the center of the universe. 
It presses not only upon the caloric atoms within, but 
inwardly upon the caloric mass from Avithout. Thus the 
ether's pressure may be said to be to the caloric what gravity 
is to the Earth's atmosphere and gives it tlie same form. It 
diminishes the elasticity or expansive force of the caloric 



HEAT AND ELECTRICITY. 21 

not only by pervading its pores and retarding the repulsion 
of its atoms whenever they collide, but it presses inwardly 
upon the circumference of the caloric globe (for the com- 
pression of the ether would give it this shape), and sends its 
pressure by transmission through the caloric medium in the 
direction of the centre, just as the lower parts of the Earth's 
atmosphere press upon the Earth's surface, not only with 
their own gravity, but sustaining that of the parts above. 
The ether does not compress the caloric as the atmosphere 
compresses water, by a pressure which is wholly external, nor 
does it diffuse itself freely through the caloric, as gases are 
diffused. But its action is of a kind intermediate between 
these : it pervades and compresses at the same time. For 
in the diffusion of gases, as well as in the mixture of liquids, 
there is some attraction between the heterogeneous mole- 
cules, or, at any rate, less repulsion than there is between 
molecules of the same kind. This aids the diffusion. But 
in the case of ether and caloric, no relation of this sort 
subsists. We cannot infer from the above considerations 
that the same stability exists in the density of the caloric as 
apparently exists in the atmosphere of the Earth. They 
rather imply, as far as we can see, that the density of the 
caloric is always diminishing, and that the caloric globe is 
forever expanding. But since the perception of natural 
changes always grows less Avith the increase in magnitude of 
the masses in which any change occurs, whether we suppose 
the ether to exercise a pressure upon the caloric globe 
capable of controlling its dimensions, or whether we suppose 
that it goes on eternally expanding and enlarging, the effect 
is the same so far as the phenomena of gravity are concerned^ 
provided the ether and caloric have that varying density 
explained in this hypothesis. 

We have now proceeded so far in explanation of gravity 
as to have assigned a cause for that condition of ether repre- 



22 A THEORY OF GRAVITATION 



sented in the hypothesis of Sir Isaac Newton; but, at the 
same time, we have introduced another medium throughout 
space in the opposite condition, and it might at first view be 
supposed that the pressure of one fluid would counteract 
that of the other, and that, if, as Sir Isaac Newton supposed, 
the ether in the condition represented would produce impul- 
sion, the caloric, in the reverse condition, would produce 
repulsion to an equal amount. This would obviously be the 
case if the two fluids possessed the same elasticity, and the 
caloric pressed from the center with the same expansive 
force with which ether presses to the center; but this is 
contrary to the hypothesis, and I have supposed the force of 
gravitation to be the ether s excess of expansive force. 

In their relations as distinct media, the ether will be 
found as represented in the hypothesis of Sir Isaac Newton, 
and will increase in density from the center of the universe 
outwards; the caloric, on the other hand, will be represented 
by a globe of fluid having its center at the universe and 
increasing in density as its center is approached, and par- 
taking in its nature of solidity, inasmuch as there is a 
cohesion between its particles produced by the pressure of 
the ether. It is only relatively, how^ever, and on account of 
its having less elasticity than ether, w^iich alone is a perfect 
fluid, whose particles have no sort of attraction either for 
themselves or any other species of matter, that caloric can 
be compared in any respect to a solid ; for, as I have regarded 
it as the medium of radiation, it must be very elastic, and 
presents also but little obstruction to the motions of the 
heavenly bodies. And yet, in the relations of ether and 
caloric, we may reason upon one of them as a fluid and the 
other as a solid, because the elasticity of one is greater than 
that of the other and because one has cohesion and the other 
not. By taking this comparative view of ether and caloric, 
gravitation may be described as a form of cohesion, and as 



HEAT AND ELECTRICITY. 23 

this appears to be the easiest way of presenting the subject, I 
will adopt this plan first. 

We have explained that cohesion between the particles of 
matter, may be effected by the pressure of ether. We sup- 
posed these particles to be solid. But we have thought it 
allowable, also, to view the caloric relatively as a solid body 
on account of the superior fluidity or elasticity of the ether. 
We may thus conceive two globes of caloric as solid bodies, 
held in cohesion by the pressure of the ether or mashed and 
compressed together, or we may conceive of a solid body held 
in cohesion with a globe of caloric. For, by the compressive 
force of the ether, the caloric is rendered somewhat in the 
nature of a solid mass, its particles having the property 
of cohesion in a slight degree, and ifcs nature approximates 
more and more to that of a solid as we move in the direction 
of its increasing density or towards the center. Therefore, 
in whatever part of the caloric any dense body is placed, the 
caloric mass conceive I as a solid, to which the dense body 
may cohere or be pressed by the ether, would be on that side 
of the body which is next to the center of the caloric mass, 
which, in the present consideration of the subject, is the 
centjr of the universe. Therefore, the dense body being 
pressed as in cohesion to the caloric globe, would continually 
move towards its center; for the caloric mass may be con- 
templated as a solid body, whose circumference is continu- 
ally giving way at the point of contact with the gravitating 
body, and yet continually presenting a new surface on that 
side of the dense body which is next to the center of the 
caloric globe. 

We illustrated the cohesion of atoms produced by the 
impulsion of ether by that species of cohesion which may be 
effected between two bodies by the pressure of the atmos- 
phere. This sort of cohesion takes place not only between 
solid bodies, but occurs also between liquids. The different 



24 A THEOJIY OF GRAVITATION, 

degrees of cohesion between the particles of water, which 
boils at a lower temperature on the mountain summit than 
at the level of the sea, are due to this cause — so that it is not 
necessary that the bodies between which this sort of cohesion 
is produced should be solid. Indeed, there is no such thing 
as a perfect solid in nature, except the simple atoms, of 
which all bodies are composed. All other bodies which are 
masses of atoms are only relatively solid, according as they 
are more or less pervaded by the ether and caloric and 
affected with cohesion between their molecules or atoms. 
Gravity is cohesion between masses produced by the pres- 
sure of ether ; but it is necessary that one of these masses 
should be a globe of caloric, for when dense and solid bodies 
come in contact, gravitation gives place to cohesion itself, a 
more intense form of compression. All bodies except solids, 
when brought in contact, nmst be compressed and flattened 
at their points of contact by the impulsion of the ether, and 
if the masses brought in contact be fluids of the same kind, 
they will unite and form a single body. The more nearly 
the bodies approach in nature to a perfect solid, the greater 
will be their cohesion; but yet even two globes of caloric, if 
we suppose such brought in contact, would be affected with 
the property of cohesion, not only between their atoms, but 
between their masses; and the two masses would be com- 
pressed together until they became converted into one. Two 
such masses surrounding two dense bodies might in this way 
produce gravitation, and as all dense bodies at a distance 
from one another would be thus enveloped in globes of 
caloric, we have a reason both for this property's acting at a 
distance and for its being universal^ that is, affecting all 
matter except the agents themselves, the imponderable 
fluids. 

There is another way of explaining the reactions of ether 
and caloric in producing gravitation. We know that water 



HEAT AND ELECTRICITY. 25 

and air always press hardest in those parts where they are 
densest. Therefore, water always rushes with most violence 
from the lowest parts of a cask, and the air presses most 
heavily near the surface of the Earth. It is by the pressure 
of the atmosphere in this way upon their lower parts, that 
light bodies are thus buoyed up. The balloon rises upon 
this principle; and so does flame, which is burning gas, 
carrying with it the solid particles which it contains. Also 
the pressure w4iich the atmosphere exerts upon auy body 
varies with the amount of surface which is presented, being 
about fourteen pounds to the square inch of surface. ]\Iore- 
over, upon light bodies, as a balloon for instance, the 
pressure of the atmoaphere is upward in a straight line, 
being exactly opposite to that of gravity. If a body be 
placed in a globe of caloric, it would be acted upon in the 
same manner a^ the atmosphere acts upon the balloon, and 
would therefore have a tendency to move from the center of 
the caloric. But this tendency would be counteracted by the 
ether, which is densest where the caloric is rarest; and since 
the ether is a more elastic fluid than the caloric, it would 
press or impell the body in a straight line to the center of 
the caloric, and the strength and intensity of this impulsion 
would depend, first, upon the difference of elasticity between 
the two fluids, secondly, upon the amount of surface pre- 
sented by the gravitating bodies, and thirdly, upon their 
distance from one another. The cause of gravitation to the 
centre of the universe upon the hypothesis of two fluids of 
unequal density and expansive force has now been explained, 
and the law of gravity follows of necessity that bodies are 
attracted and the force varies directly as their mass and 
inversely as the squares of their distance. 

I have supposed the center of the Universe to be the 
common center of one grand system, to which the whole 
heavens gravitate, and around wh'ch they revolve. This 



26 A THEORY OF GRAVITATION, 

supposition, however, was not esssential to the support 
of our double ether hypothesis. We might have sup- 
posed separate caloric globes for each solar system, and 
thus denied any gravitating connection between the Sun 
and Stars. Proceeding upon this less extensive plan of 
viewing the law of gravity, Ave come to the question, 
which is now to be answered, how the Earth, impelled 
to the Sun, becomes itself a center of gravity? Why 
does the Moon gravitate to the Earth, and w4iy does any 
body gravitate to the Earth ? In other words, what is the 
cause of Universal gravitation'^ 

This may be attributed to two causes: First, to the projec- 
tion of the Earth around the Sun ; and, second, to the law of 
inertia. These forces would resist the impulse of the ether, 
and by arresting it cause the caloric to become denser around 
the gravitating body. Supposing the Earth or any other 
planet to be this body, the condition of the caloric around it 
is rendered by its projection like that about the Sun, in- 
creasing in density as we approach. The Earth being solid, 
and not elastic, the ethereal pressure is not transmitted 
through its substance to the caloric on the opposite side, but 
terminates upon its surface. Hence the ether will be made 
to react noon the Earth on the side next to the Sun, and on 
every other side, so that it will press inwardly upon the 
Earth in all directions, and compress the caloric to it. This, 
however, would not happen, if the Earth had not its projectile 
motion, but moved with the full force of its gravity to the 
center of the caloric mass, which is now supposed to be oc- 
cupied by the Sun. But this free motion is impossible on 
account of the law of inertia. Thus the Earth and other 
planets become centers of gravity, since this condition of 
caloric cannot exist without it. It is also plain that, if the 
planets become centers of gravity by virtue of their projectile 
forces and inertia, that the Sun may, in like manner, become 



HEAT AND ELECTRICITY. 27 

a center of gravity, to which the planets are impelled, by vir- 
tue of a motion around the center, or some other point of 
the universe. In like manner, the satellites of the planets 
may receive the same property from similar conditions. All 
other bodies of sensible or common matter likewise become 
centers of gravity, and come under the law of universal gravi- 
tation, by resisting the impulse or pressure of ether, whether 
by the projectile motion above mentioned in connection with 
the Sun, planets and lesser satellites, or whether by that 
property alone which is called inertia. For it is impossible 
that the force or momentum stored in a falling body of 
matter by inertia should impart to it a velocity as great as 
that of the impulse ; and, if it be less, it must cause the body 
to which it falls to gravitate by intercepting the pressure of 
the ether. 

Accepting the above theory, the laws of gravity seem to 
follow of necessity. The laws are : First, that gravity acts 
instantaneously; second, that its action between two bodies 
is not intercepted by the intervention of a third body; third, 
that bodies are attracted directly as the mass, without re- 
gard, to the qualities of the substance ; and fourth, that the 
intensity of the force varies inversely as the square of the 
distance. The first of these properties is explained by the 
supposition, that the two ethers have constantly, at all points, 
such a relation to each other, that the bodies are reacted upon 
by a power in their immediate vicinity, and not by the body 
in the distance, by which they are supposed to be attracted. 
We readily see, too, from the same theory, why the attraction 
between any two bodies is not affected by the interposition 
of a third body. The third property is explained by the sup- 
position, that the particles of matter are not in contact, but 
that there are considerable inter-spaces between them, and 
that the action does not take place immediately between the 
masses, but between the particles of masses, so that when a 



28 A THEORY OF GRAYITi^TION, 

body gravitates to the Earth, its gravity is the sum of the 
weights of all the particles, and the weight of each particle 
depends upon its volume or the space which it occupies, and 
not on any peculiar gravity of the substance; for if the 
pressure of the ether is supposed to operate in straight Imes 
from a circumference to a center, it is obvious that a large 
body would obstruct more of this pressure, than a small 
body. In like manner the amount of pressure would be 
affected by the position of a body from the center of gravita- 
tion^ as well as by its magnitude. For it is also obvious, 
that a body near the center would cut off or intercept more 
of the pressure, than a more distant body, and that the amount 
intercepted, or the intensity of the gravitating force, would 
follow the same law of inverse squares as the intensity of 
light and heat; for I suppose the force of gravity to act in 
straight lines to a center, while these forces act in straight 
lines from the luminous body. 

The cause of gravity between masses and that attraction 
which takes place between particles of matter at insensible 
distances is the same; the latter being modified, however, by 
the action of heat, and it may be also by electricity. In re- 
gard to the attraction, which exists between the pai tides of 
matter, a distinction is made between that which acts be- 
tween molecules and that which acts between atoms or the 
primary elementsof bodies, the latter being designated c/^^em- 
ical affinity^ and the former coliesion and adhesion— goIiq^iow, 
when the molecules are of the same kind, and adhesion, when 
the molecules are unlike. Thus, we have three kinds of at- 
traction or impulsion — gravity between masses, cohesion and 
adhesion between molecules, and affinity between atoms. 
The intensity of this impulsion is greatest between atoms, 
and least between masses. But, besides this impulsion, there 
is a repulsion, heat, which operates also between masses, mole- 
cules, and atoms, and follows the same law of intensity, being 



HEAT AND ELECTRICITY. 29 

greatest between atoms, next greatest between molecules, and 
least between masses. We may illustrate the difference of 
what is meant by cohesion and affinity by the difference, 
which exists between a compound and a mixture. 

From what I have stated of tlie laws of impulsion and re- 
pulsion, the action between molecules must be weaker than 
between atoms, not only combining with less force when they 
attraoiif^ but also repelling one another with less force when 
under the influence of heat. But there is a much stronger 
resemblance between the actions of molecules and atoms 
than between masses and molecules, so that cohesion cannot 
be said to hold an intermediate place between affinity and 
gravity ; for so great is the resemblance between the action 
of the former two, that it is sometimes difficult to distin- 
guish a mixture, which depends on the interaction of mole- 
cules, from a compound which results from the affinity of 
atoms. With regard to atoms, some elements unite to form 
compounds, and others do not; some unite readily and with 
great force, others only under peculiar circumstances. So 
with regard to molecules ; some substances mix, others do 
not. Substances cannot mix but in the liquid or gaseous 
form, when the molecules of the same substance have a 
greater repulsion for one another, than for the molecules of 
the substance with which they mix, or through which they 
are diffused. In a mixture the force of adhesion is greater 
than that of cohesion. When the atoms of one substance 
come into the neighborhood of some other substance, for 
which they have a stronger affinity than for themselves, a 
compound is formed, and the compound is stronger or weaker 
in proportion to the strength of a.inity between the hetero- 
geneous atoms. The same is the law of mixtures. Their 
strength depends upon the strength of attraction between 
heterogeneous molecules. Diffusion of gases does not de- 
pend upon attraction or impulsion, but upon heat or repul- 



30 A THEOEY OF GRAVITATION, 

sion. Gases are diffused, because there is a stronger repulsion 
between the molecules of the same kind in the state of gas, 
than between unlike molecules. This belongs to the subject 
of heat, which I will discuss in the subsequent chapter. 
So closely are the two forces of heat and attraction associated 
in all chemical action, that one cannot be well separated from 
the other. A correct theory of chemical attraction cannot 
be formed without a corresponding theory, at the same time, 
of the nature of heat. 



CHAPTER III. 

heat; or, the kepulsive forces of matter due to a rota- 
tory MOTION OF ATOMS AND MOLECULES, AND TO 
THE EFFECT OF SUCH MOTION UPON 
THE INTERSTELLAR MEDIUM. 

As gravitation requires a projection of masses to counter- 
balance its tendency in the plan of the Solar system or the 
Universe, so chemical attraction requires a counteracting mo- 
tion of atoms and molecules as a necessary condition in the 
constitution of terrestrial substances. The theories regard- 
ing the nature of these movements have been various. Some 
suppose that the movement of molecules in liquids and solids 
is of an oscillatory character, and that in the gases the par- 
ticles are entirely free. It is supposed that the elasticity of 
the gases is due to the incessant bombardment of their loose 
molecules one against another. Another view is, that the 
motion resembles that of the planets on their axis, and that 
atoms or molecules so revolving on their axis may assume 
three positions in regard to one another, which determine the 
three conditions of matter as solid, liquid, or gas. The 
second view is the one which I shall adopt to explain 



HEAT AND ELECTRICITY. 31 

chemical action and the attractions and repulsions of mole- 
cules, Avhile the vibratory motion is that of radiation. 

That the atoms and molecules of gaseous bodies should 
be entirely free in their motions, and that their elasticity is 
due to the incessant bombardment of the particles against 
one another, and against the vessels which contain them, is 
at variance with the hypothesis, which I have presented of 
gravity — that, whenever two particles of matter come in con- 
tact, they are immediately acted upon by the compressive 
force of two powerful fluids, which tend to hold them to- 
gether. It is also at variance with the ordinary law of 
gravity, which is, perhaps, the same for chemical affinity, 
that attraction acts instantaneously. If this principle be 
true, the particles could not collide and, at the same time, be 
free. For a number of reasons, which I will mention, this 
view of heat seems to me untenable. Can we suppose, for 
example, that if the particles of gas were perfectly free in 
their movements, and moved with vast velocity, without 
any law to control or direct them, that they would always 
preserve the same distances between them ? Would not the 
volume of any gas, if its molecules moved in so loose a man- 
ner, be denser in some parts, than in others? Again, when 
we consider the immense pressure of confined and condensed 
gas, and the enormous velocity of its molecules, which pro- 
duces this pressure, can we suppose, if these molecules were 
free and moved in straight lines, and were projected like 
cannon balls against the sides of the vessel containing them, 
that the particles would not escape through the pores of 
almost any substance, that could be employed to confine 
them ? What substance, that cannot withstand the bombard- 
ment of cannon balls, would be not pierced by the bombard- 
ment of gaseous molecules, which are of greater weight in 
proportion to their magnitude and move with greater velocity, 
if we suppose them to move in straight lines? Such a 



32 A THEORY OF GRAVITATION 



view of heat seems also to conflict with what appears to be 
the best explanation of the chemical activity of gases, in what 
is termed their nasceiit state. Nitrogen makes compounds 
with oxygen, hydrogen and carbon ; but these cannot be ob- 
tained by simply mixing the gases. The air is chiefly a mix- 
ture of nitrogen and oxygen ; yet these gases never combine 
in that state, because their particles are out of range of 
chemical affinity, and have to be brought nearer together. 
In order to make them combine, they must be united in their 
most concentrated form, which occurs at the time of their 
separation from some other compound. The explanation 
given of this phenomenon is, that in the nasce?it state the 
particles of the gases are brought nearer together, than it is 
possible to bring them by any mechanical pressure when 
mixed as gases. This would not be true — it would be no 
explanation at all— if the expansion of the gases is due to a 
collision of their particles ; for their condition would then be 
always that of their nascent state; they would be coming 
continually within the influence of one another's attraction. 
I suppose, therefore, that molecular repulsion, whether it 
occur among the atoms and molecules of a solid, a liquid, or 
a gas, is in every case due to the rotation of these particles, 
and to the efl'ect of this rotation upon the condition of the 
imponderable medium which surrounds them. As to the 
spaces or distances between atoms, I suppose them to vary 
according to the nature of matter, or rather the magnitude of 
atoms and the intensity of their motions. I suppose the 
atoms of ether to be in contact and colliding instantaneously. 
The proximity of the caloric atoms is also greater than in 
ponderable matter, but nevertheless separated by spaces, 
which vary with their cohesion. The atoms of ponderable 
matter I suppose to be separated by much greater spaces, and 
revolving each on its axis, in an atmosphere of caloric and 
ether, like little worlds. The elasticity of ether and caloric 



HEAT AND ELECTRICITY. 33 

would be due to the rotatory motions of atoms in actual con- 
tact or instantaneously colliding; but the atoms or mole- 
cules of ponderable matter do not repel one another by 
actual contact, but through the effect of their rotatory mo- 
tions upon the caloric atmospheres surrounding them. 

The elastic force of ether and caloric would be uniform in 
each; but there are several conditions of ponderable matter, 
in which cliemical repulsion and chemical impulsion, taking- 
place between the particles of ponderable matter, would vary. 
Some of these circumstances I will mention, which will cause 
me to modify, to some extent, the prevailing theories of heat; 
so that instead of defining it as a fluid exclusively, or a force 
exclusively, I will consider the phenomena of heat as the 
combined effect of fluids and force. 

The science of chemistry now makes a distinctiou between 
atoms and molecules. An atom is the smallest particle of an 
elementary substance ; as an atom of hydrogen, or an atom of 
oxygen. A molecule is the smallest particle of a compound 
substance, as a molecule of water. I make a distinction in 
the motions of atoms and molecules. That of an atom is 
inexhaustiile ov infinite; that of a molecule is subject to 
change. The expansion of ponderable matter, which takes 
place during healing, may be effected in one of several ways : 
First, by increasing the motion of molecules; second, by 
changing the positions of atoms or molecules relatively to 
one another ; thirdly, by increasing their atmospheres and 
prizing them apart by the inflowing of double ether or fluid 
heat. Hence, the term heat embraces the complex idea of 
motion and position of atoms and molecules and the condition 
of the double ether or fluid heat around them ; and since chem- 
ical repulsion is always the effect of the rotatory motion of 
atoms and molecules upon the double ether around them, we 
cannot possess a clear idea of the phenomena by considering 
one without the other. 



34 A THEORY OF GRAVITATION 



We may, therefore, first consider the effect of motmi upon 
the double ether, and afterwards the effect of position; for in 
some positions I conceive that the effect of the motion upon 
the atmospheres of molecules is different from what it is in 
others. We have supposed a slight cohesion to subsist 
between the atoms of caloric, arid that none exists between the 
particles of ether ; and, hence, Ave supposed, that the motions 
of the heavenly bodies are resisted by their friction against 
the caloric, and not against the ether. This friction, how- 
ever, Ave supposed to be very slight, and hence its effect on 
the motions of the heavenly bodies is very little; but it must 
increase Avith an increase in velocity, and bodies moving very 
rapidly through the caloric must OA^ercome more friction 
than other bodies moving Avith less impetus. As this fric- 
tion produces some effect upon the velocity of the body moving 
through the caloric, Ave must admit, in accordance Avith 
the principle of conservation, that it must also have some 
effect upon the caloric, although in regard to the motion of 
the heavenly bodies it may not be so easy to see Avhat this 
effect on the caloric may be. In the case, however, of atoms 
and molecules, Avhich are supposed to move on their axis 
with inconceivable velocity, Ave may suppose, that the friction 
of the atom against the caloric is very considerable, and we 
may, in this case, form some conception of Avhat the effect 
of this friction Avould be, not only upon the atom or mole- 
cule, but also upon the caloric atmosphere surrounding it. 
For, if there exists cohesion, hoAvever slight, between the 
caloric atoms and none betAveen those of ether, the rotatory 
motion of the ponderable atoms AA'^ould have more effect in 
repelling the caloric, than in repelling the ether. Hence it 
is plain, that the caloric atmosphere surrounding a rotating 
atom or molecule, instead of following the general laAV of im- 
pulsion by becoming denser as Ave approach the gravitating 
body, Avould be made by the friction to fly off from the ro- 



HEAT AND ELECTRICITY. 35 

tating atom, so as to increase outwardly in density for some 
distance from the atom. This would be a reversion of that 
condition of the caloric atmosphere, which has been described 
as necessary to produce gravity or impulsion, and the extent 
of this reversion would increase with the velocity of the atom 
or molecule, and with the friction consequent thereupon. 
Now the condition necessary to produce gravity or impul- 
sion requires the caloric to increase in density, as the dis- 
tance from the gravitating body is diminished, in order that 
the impulsion of the ether may be greater on the farther, 
than on the contiguous sides of any two or more gravitating 
bodies. If, therefore, this condition of the caloric is reversed 
around atoms and molecules by their rotatory motions, it 
must be plain, that atoms would gravitate from each other 
instead of being impelled to each other, and that molecular 
repulsion must predominate over the opposite force, w^herever 
this reversed condition is supposed to exist. At those parts 
where the impellent and repellent conditions of the caloric 
atmospheres run into each other, the gravitating atoms or 
molecules would be held in cohesion, although their surfaces 
never come in contact. 

If, now, we suppose a mass of ponderable matter consisting 
of many atoms and molecules to have the same affinity sub- 
sisting between each and all of these elementary particles, it 
is plain, that they would all assume and maintain by virtue 
of their impellent and repellent forces equal distances apart 
(nor would one atom or molecule collide with another), un- 
less some were subjected to greater pressure than others, as 
is the case in the gases composing the Earth's atmosphere. 
At a great distance from the Earth the gaseous molecules in 
the upper regions of the atmosphere may have a cohesion as 
well defined as that subsisting between solid bodies; and 
even upon the Earth's surface the impellent and repellent 
forces of the gaseous molecules are so adjusted during ex- 



36 A THEORY OF GRAVITATION, 

pansion and diffusion as to serve as a law in preserving the 
same density in all parts ; so that tlie pressure of gas upon 
the sides of any vessel, in which it may be confined, is due 
not to the random pelting of the gaseous particles, but to 
their uniform repulsion through their caloric atmospheres. 
We see, now, how the atoms and molecules repel one an- 
other by the effect of the motions, and how the expansion of 
masses is thus produced. Let ns inquire what partis acted 
by fluid heat or double ether apart irom what has been said. 
We suppose all space to be filled .with matter. Hence, when 
a vacuum might be caused by the expansion of bodies in 
heating, the double ether, or heat fluid, flows into the 
dilating pores as the particles of the mass are parted by re- 
pulsion. During expansion there must be a deficiency of 
fluid heat in every expanding body, and hence it must ex- 
tract it from surrounding sources. I think it may be 
shown, that there are cases when the extraction of fluid heat 
from a body produces cold, and its absorption produces 
warmth, without decreasing the rotatory motion of atoms in 
the first case, or increasing their rotatory force in the latter. 
If we confine a body of gas, and subject it to pressure, it 
will throw off, by conduction, a part of its fluid-heat, but 
does not lose any of its atomic motion. If we remove the 
pressure, the gas, by virtue of its atomic motion, wdll absorb 
again the same amount of fluid-heat which it had before; 
and its temperature, in either case, under the diminished or 
increased pressure, will be the same as that of surrounding 
bodies. But during the expansion of the gas, surrounding 
bodies are cooled; and during the contraction of its volume 
they will be heated. These changes, I conceive, take place 
not by the passage of force, but by the conduction of fluid- 
heat. It is true, force is expended in administering the 
pressure, but it is expended against the impulsion of the 
molecules of surrounding substances in prizing them apart 



HEAT AND ELECTRICITY. 37 

with the fluid-heat expelled from the coilipressed gas, and it 
is not converted into their molecular motion ; for, although 
it continues to act after the contraction, no heat is produced* 
The pressure is balanced by the repellent forces of the 
gaseous molecules and the impellent forces of the particles 
of the confining vessel and surrounding matter. When we 
explode gunpowder, the atoms do not acquire any new im- 
petus or velocity in the gaseous form. They simply assume 
positions more favorable for expansion; and the sudden ex- 
pansion of the mass, upon conversion into gas, compresses 
the atmosphere and absorbs the two ethers or fluid-heat, 
which the compressed atmosphere throws out. Thus the 
phenomena of heat are seen under two aspects, as force and 
as a fluid. 

The atoms of simple gases never acquire or lose velocity, 
but have movements as uniform as those of the heavenly 
bodies; but the motions of molecules depend upon heat 
force, and have a greater velocity in the form of vapor, than 
in that of a liquid or solid. The only efl'ect of heat on 
atoms is to alter their positions or change the directions of 
their motions; but on molecules it not only changes posi- 
tion, but imparts motion. Hence the motions of atoms and 
molecules must give rise to distinct phenomena. But for 
the purpose of pointing out the relations of the heat force and 
the heat fluid, the vapor of water may be used in place of the 
fixed gases. This is seen in the effect of pressure on the 
boiling of water, which boils at a lower temperature at high 
elevations, than at the level of the sea. In the toiling of 
water heat- force, and not heat-fluid, raises the vapor. There 
is an increase of motion in the watery particles. But the 
same amount of motion will not produce steam at every 
elevation. The external pressure of the atmosphere acts as an 
increment to molecular cohesion, and, therefore, the heat 
necessary to raise steam must vary with this pressure. Hence 



38 A THEORY OF GRAVITATION, 

steam formed at a low elevation has a higher temperature, 
more molecular repulsion, and greater elasticity, than steam 
formed at high elevations. The pressure, therefore, in this 
case does not dimmish the rotatorv force of the molecules, 
which continue to increase in force as long as heat is applied ; 
but it simply prevents the inflow of fluid-heat or double 
ether, which is necessary to expansion. 

There are three well-marked conditions of matter; the 
solid, the liquid, and the gas. For these three states, three 
positions of atoms or molecules have been assumed, suggested, 
perhaps, by the effects of currents of electricity, which in some 
positions attract, and in others repel. For the solid form we 
may supp jse any two atoms or molecules to have their axis 
parallel and to rotate in the same direction. This causes 
the rotatory motion of one atom to neutralize the eff'ect of 
the rotatory motion of the other atom upon the intervening 
caloric. They would, therefore, be impelled to one another 
as if neither moved. For the liquid form, we may suppose 
the same two atoms or molecules to be partly turned, so as 
to have their axis at right angles. For the gaseous form, the 
atoms are supposed to have their axis parallel and to rotate 
in opposit3 directions. 

I have already partially explained the effect of the rotatory 
motion of atoms upon the double ether surrounding them. 
But we have thus far considered the effect of the rotatory 
motion of an atom only upon its own caloric atmosphere. 
We must now examine into the effect of the rotatory motion 
of one atom upon the caloric atmosphere of another atom, 
according to the positions, which thoy occupy towards one 
another. We have shown that around an atom at rest the 
caloric atmosphere increases in density as it is approached. 
This condition produces impidsion. And we have said that 
the rotation of the atom would repel the caloric, reverse the 
condition, and ])Yo(}i\\GQ repidsion. But we must say a word 



HEAT AND ELECTRICITY. 39 

more on this point. The rotation of the atom would not 
only repel the caloric, but it would repel it in a direction 
somewhat corresponding to its own motion, as we see the 
sparks fly from the revolving stone of the scissors-grinder. 
Now, if two atoms be placed and move, as we have supposed 
for the solid form of matter, their contiguous surfaces would 
move in opposite directions, and would repel the caloric in 
opposite directions; so that, while each would tend to rarify 
its own caloric atmosphere, it would make that of the other 
denser; for the caloric which is repelled from one atom will 
be met and repelled by that which is repelled from the other. 
Hence the effect of one's motion would be counteracted by 
that of the other's motion, and they would be held in 
cohesion. It is easy now to see, how in the third or gaseous 
form, where the atoms move in opposite directions and their 
contiguous suTfaces in the same directions, that the repulsion 
of one would assist the repulsion of the other, and that in 
the secohd position, that for liquids, they would neither 
oppose nor assist. 

There are many circumstances of form, magnitude, motion, 
and position which may afiect the chemical quanti valence of 
atoms, but,' it is probable that the conditions of masses 
depends" -more on the relative , positions of the particles 
constituting them than upon the increase or decrease of 
their motions; and we may readily conceive that a body may 
exist in the solid, liquid, or gaseous form by simply altering 
the direction, without altering the amount of motion of the 
atoms or molecules. In corroboration of this opinion, water^ 
in its three forms, may serve us with a good example. As 
long as the relative positions of the aqueous molecules 
remain unchanged, the condition of the body as ice, water, 
or vapor, remains the same, notwithstanding it may vary 
many degrees in temperature. What then sustains the 
aqueou's molecules upon the two "precipices," to use a figure 



40 A THEORY OF GRAVITATION, 

of TyndalFs, from which they fall so suddenly in their 
conversion from steam into water, and from water into ice, 
unless it be these relative positions ? 

I propose to discuss the polarity of atoms and molecules 
under the subject of electricity. Bat there is one fact which 
it is well to note here. All points on the surface of a rotating 
atom do not move with the same velocity. It must be 
admitted, then, in considering the effect of the rotation of 
a single atom upon its own atmosphere, that there would 
always be two points upon its surface, namely, the two poles 
of its axis, to which the impulsion would be stronger than 
to other points, and the repulsion of the atom would be 
greatest in parts about its equator, where the rotatory motion 
of the atom would have the greatest effect in rarifying its 
atmosphere. Form, magnitude, and velocity combine to 
vary the polarity of atoms and to control their aggregation 
in molecules. Then the centrifugal motion of the molecule, 
imparted by heat, reacts against the polar forces of the 
atoms and may shiver the molecule again into its elements 
or change its form. A rapid revolution on its axis might 
elongate the equatorial diameter of the molecule, and this 
result would vary not only with the rapidity of the mole- 
cular motion, but with the strength of the polar forces of 
the component atoms ; for by their composition some mole- 
cules might be more compact than others. The change 
produced in the form of the molecule by heat, might produce 
a change in a mass of such molecules. The expansion in 
the mass produced by heat may correspond with the expan- 
sion produced in the molecule. The same amount of 
centrifugal force may expand a compact molecule less than 
one whose aggregation is more complex, and, therefore, 
weaker; and the same amount of heat may expand a mass of 
this first sort of molecules less than a mass of this second 
sort. It may be from some such cause as this that some 



HEAT AND ELECTRICIXy. 41 

bodies expand more than others in being raised through the 
same temperature, and that some bodies are chemically 
affected by heat more than others. 

But the fixed gases, which are all constituted alike, 
expand equally in passing from one degree of temperature 
to another. A volume of oxygen or nitrogen will overcome 
the same pressure as an equal volume of hydrogen in 
coneuming the same quantity of heat. Hence, upon the 
comparison of gases by volume, their capacity for heat is the 
same; but considered in regard to weight, their specific 
heat, or capacity for heat, increases as their weight is 
diminished. The products of the weights and specific heats 
of the atoms of elementary substances are generally equiva- 
lents. The measurement of atomic weights is found by 
reducing the substance to the state of gas or vapor, and is 
based upon the hypothesis, first enunciated by Avogadro in 
1811, and by Ampere in 1814, that equal volumes of all 
substances, when in the state of gas, and under like condi- 
tions, contain the same number of molecules. If we take 
any two or more such equal volumes, as hydrogen and 
oxygen, it will be found that the hydrogen will weigh only 
one-sixteenth as much as the oxygen, and hence the 
hydrogen atom is said to weigh one microcrith, and the 
oxygen atom is said to weigh sixteen microcriths. If we 
examine these equal volumes with regard to their specific 
heats, or the amount of heat necessary to raise them through 
the same number of degrees of temperature, we shall find 
that the amounts for the two volumes are nearly equal. 
Hence it requires nearly the same quantity of heat to raise 
sixteen microcriths of oxygen as it requires to raise one 
microcrith of hydrogen through the same number of degrees 
of temperature. Hence we must infer, either that the heat 
force of the sixteen volumes of hydrogen is sixteen times 
as great as that of the one volume of oxygen, or that the 



42 A THEORY OF GRAVITATION, 

molecular impulsion of a volume of oxygen is sixteen times 
as great as the impulsion of an equal volume of hydrogen at 
the sanle temperature. One only of these alternatives can 
be true; and the latter I assume to be correct. Hence it 
appears that with one-sixteenth of the impulsion (for a 
hydrogen atom is only one-sixteenth as heavy as an oxygen 
atom), and with equal repulsion, hydrogen would absorb 
sixteen times as much double ether or heat fluid as oxygen. 
There are two causes which co-operate to produce the 
expansion of bodies. Heat force, by increasing the circular 
motion of molecules, would cause expansion. Again, expan- 
sion might be produced by increasing the double ether or 
densifying the caloric composing the molecular atmospheres. 
A body is heating when it is expanding by any of these 
modes. When we compress gas, we cool the gas and heat 
surrounding bodies, not by diminishing the molecular 
motion of the one, or increasing that of the other, but by 
producing a flow of the heat fluid or double ether. The 
double ether is pressed out of the gas and into surrounding 
bodies, so that these expand as that contracts. The gas, 
however, has not lost molecular motion by the process, nor 
have surrounding bodies acquired it. As soon, therefore, 
as the pressure is removed from the gas, its molecular 
motion causes it to expand, and this expansion abstracts 
from surrounding bodies the double ether, which had been 
imparted to them by the compression of the gas. There- 
fore, the gas is capable of producing, by its expansion, a 
degree of cold corresponding to the amount of heat emitted 
while its volume was being contracted. The flow of the 
heat fluid in each of these two cases depends upon the same 
principle, the plenum of space. When, therefore, we reduce 
a mass of ponderable matter to a smaller volume, we expel 
the double ether which fills its pores; when we enlarge its 
volume we increase its capacity for the interstellar medium. 



HEAT AND ELECTRICITY. 43 

which is, therefore, absorbed. The pressure which reduces 
the yolume of the gas, and the molecular force which 
expands it, are the energies in the above example, which 
produce the ebb and flow of the interstellar medium. 

In every heating effect two agents are to be considered — 
the heat force and the heat fluid. The movement of the 
heat fluid is called conduction^ and it is found to take place 
through some arrangements of atoms and molecules more 
readily than through others. Let us suppose two volumes 
of gas to be submitted to the same pressure, and surrounded 
one by good conductors, and the other by imperfect con- 
ductors. It seems reasonable to suppose that the gas 
surrounded by the good conductors Avould be more com- 
pressed than the gas surrounded by the non-conductors. 
At the same time, since it is probable, that ether would 
flow, on account of its greater rarity, more readily through 
the non-conductor than the caloric; the caloric would, 
probably, be found more dense in the volume of gas 
surrounded by the non-conductor than in the volume 
surrounded by the conductor. This diflerence of caloric 
density in the two volumes is the cause, I suppose, why one 
volume would be more compressed than the other. For I 
have supposed expansion to be produced not only by 
increasing the amount of the double ether, but by densifying 
the caloric; in fact, I suppose this thickening of the caloric 
to be one means of increasing the amount of the double 
ether constituting the molecular atmospheres; because it 
would seem that the same rotatory motion of the molecules 
must produce a more intense repulsion through a dense 
medium than through a rarer, since against the former the 
friction of the molecule would be greater. 

If we should connect the two volumes of gas by a con- 
ductor, it is probable that the caloric would' flow through 
it from the insulated gas to the uninsulated, and a 



44 A THEORY OF GRAVITATION, 

current of ether would flow through the conductor in the 
opposite direction. If we could suppose the insulators and 
conductors perfect, then the strength of the current flowing 
from one volume to the other would he exactly equal to the 
pressure exerted upon the insulated gas. Calling the caloric 
positive electricity, and the ether negative electricity, the 
connection of heat and electricity may now be seen. The 
conduction of heat consists in the flow of the double ether, 
or the two fluids constituting it, in the same direction, and 
is accompanied with expansion. The conduction of 
electricity consists in the separation of the double ether 
and the flow of the fluids composing it in opposite directions ; 
and as one fluid simply takes the place vacated by the other, 
it is not accompanied with expansion. 

Both in the phenomena of heat and in the phenomena 
of electricity the same fluids and the same kind of 
motion is required, and the same arrangement of atoms and 
molecules, which constitutes a conductor or a non-conductor 
of heat, also constitutes a conductor or a non-conductor of 
electricity. 

The physical and chemical changes which are always 
taking place in the Earth aff'ord us numerous examples of 
the conversion of heat into electricity, and some of these, 
perhaps, may be explained by the experiment which I have 
supposed to be made with the compressed volumes of gas. 
It may be by a process of this sort that electricity is 
developed in the atmosphere. Vapors ascend charged with 
latent heat, which is liberated when they are converted into 
liquid and take the form of cloud or rain. Here we have 
then a body of vapor condensed and surrounded by a non- 
conductor. The vapor is in place of the gas supposed 
above ; the compressive force is developed in the physical 
change of vapor into water, and the atmosphere is the vessel 
in which the vapor is insulated. The ether, on account of 



HEAT AND ELECTKICITY. 45 

its extreme tenuity, escapes; the caloric is condensed. 
Thus the air is charged with positive electricity. An 
immense amount of electricity may be formed in the atmos- 
phere in this way from the application of steam, the steam 
being condensed, and heat converted into electricity. 

Experiment might show that if the hydroelectric machine 
were so modified as to effect a greater condensation of the 
steam, the amount of electricity collected would be much 
increased. It is usual to ascribe the generation of this 
electricity to friction of the steam upon the sides of the 
pipe through which it issues. If this were so, an immense 
amount of negative electricity would be collected on the 
sides of the pipe, for friction always produces the two kinds 
of electricity in equal amounts, and the steam could not, 
according to this principle, be made positive unless the pipe 
conducts away the negative electricity. As this appears not 
to be the case, I have conjectured that the electricity is mainly 
produced by the condensation of the steam and the conver- 
sion of heat. It is the fluid heat that is converted into 
electricity. The heat force is radiated. 



46 A THEORY OF GRAVITATION, 



CHAPTER IV. 

ox RADIANT HEAT AND LIGHT. 

I HAVE considered on the basis of the double ether 
liypothesis, the nature of heat as a mode of motion in 
ponderable matter, which I have described as a rotatory 
motion of atoms and molecules. It remains now to consider 
its nature as radiant heat, or as a mode of motion in impon- 
derable matter. Eadiant heat is the transmission of force 
from one molecule of ponderable matter to another by the 
undulation of an elastic medium. This transmission, or 
radiation, takes place by rectilineal motion, and the heating 
effect consists in the change of this rectilineal motion into 
the rotatory motion of the molecule. The molecule throwing 
out heat converts its circular motion into the rectilineal or 
undulatory motion of the interstellar medium, and the 
molecule absorbing heat reconverts this rectilineal into 
circular motion again. Thus motion lost by one molecule 
is transmitted through the interstellar medium and acquired 
by another ; and simultaneously with the communication of 
the heat force, a communication of fluid heat also occurs 
between the two particles. The body whose molecules 
acquire heat force, expands and absorbs the fluid; and the 
body whose molecules lose force, contracts and expels it. If 
no ponderable matter intervene between the two bodies, the 
double ether or heat fluid flows immediately from one to 
another. But when two or more molecules at a distance and 
separated from each other by the intervention of ponder- 
able matter lose and acquire fluid heat, the third body, 
through which the fluid heat flows or passes, is called a 



HEAT AND ELECTRICITY. 47 

conductor, and the transmission of heat through it is called 
condiiction. But of this, more by and by. 

From the nature of the law of gravity, that bodies are 
attracted inversely as the square of the distance, the velocity 
of a planet is such that the radius vector of its orbit 
always describes equal areas in equal times, whatever be its 
distance from the Sim. Therefore, the planet moves in the 
neighborhood of its perihelion with greater velocity than 
in that of its aphelion. Likewise motion and attraction 
are associated in the constitution of all material substances, 
and the attraction between their particles, when modified 
by heat, takes the form of chemical affinity. But we do 
not know the nature of the motion of these particles as 
well as we understand the motions of the heavenly bodies. 
Some philosophers have thought that heat vibrates the 
particles of matter or projects them in straight lines, some- 
what after the manner of the orbital motions of the heavenly 
bodies ; others, as Prout, in the " Bridgewater Treatises," 
whom I have followed in explaining the theory of heat and 
the three forms of matter, suppose this motion to be 
rotatory, like that of the heavenly bodies on their axis. 

Assuming that the same law of inverse squares applies 
alike to the gravitation of masses and the affinity of 
particles, Ave must infer that masses and particles are like- 
wise governed by the same laws of motion, and that as the 
more distant planets require the less velocity to sustain them 
in their orbits, so the particles of matter, as they recede 
from one another by the action of heat, require less heat 
force to carry on the further separation. If the attraction 
of particles for one another varies inversely as the square of 
the distance, the heat force necessary to sustain them in a 
state of isolation must follow the same law. The investiga- 
tion of this law then ought to throw some light on the 
nature of the motion of molecules. It seems to warrant the 



4:8 A THEORY OF GRAVITATION, 

conclusion that the heat between the particles of masses 
follows the same law of. diminution as the heat which is 
radiated between distant masses, and that the motion of 
these particles cannot be in right lines, as some philoso- 
phers have supposed them to move in the state of gas. 

If we consider the law of "the expansion of gas, that 
under a constant pressure its volume increases directly as 
its temperature, bearing in mind at the same time that its 
particles attract one another with a force which varies 
inversely as the square of the distance, Ave must conclude 
that the heat force diminishes in the same manner as the 
attractive force diminishes with the distance. This diminu- 
tion is best explained by the supposition that the heat force 
which forces apart the particles of matter is the same as 
radiant heat, and passes from particle to particle, not by 
their contact and collisions, but through the oscillation of 
the interstellar medium. The waves thus produced in the 
interstellar medium between the particles of a body being 
the same, or at least of the same nature, as the waves of 
light, the intensity of their force follows the same law of 
diminution. The waves which produce light are emitted 
from the molecules on the surfaces of masses ; but those 
waves which are emitted by the molecules within the mass, 
do not come to us so as to affect the organs of vision; 
neither do they emerge from the mass, but act between the 
molecules and endow them with such repellent properties 
as to exactly neutralize the force of attraction. This is the 
condition of bodies when they are at the point of assuming 
the form of gas or vapor ; the repellent and impellent forces 
of the particles balance one another, and the particles are 
free. Beyond this point, if the repellent force becomes 
greater than the impellent force, the j)articles recede from 
one another with a force which increases directly as the 
temperature, and the mass assumes the elastic form of gas; 



HEAT AND ELECTRICITY. 49 

but if the impellent force is greater than the repellent 
force, the body will take the solid form, and the particles 
will be pressed together with a force which varies directly 
as the temperature. Therefore, the specific heat of bodies 
varies inversely as their atomic or molecular weights, whether 
the body be in the form of solid, liquid or gas. By this 
supposition of the nature of heat, we may explain the three 
laws of Marriot, Charles and Avogadro without discarding 
the force of attraction. 

But according to the other theory, which supposes the 
particles to beat against one another, the bursting power of 
the gas would not be doubled by doubling the motion of 
its particles, unless the particles have lost all power of 
attraction for one another, and the gas's expansion is 
retarded only by external pressure. We are required to 
grant that the particles which in the state of solid had the 
property of attraction, in the state of gas are wholly 
without it ; and we are presented with no account of this 
loss which is at all satisfactory. For if this property of 
attraction acts instantaneously as the law of gravitation, it 
would certainly be unwarrantable to conclude that in the 
state of gas the particles get beyond the influence of the 
property, and at the same time assert that the expansion of 
the gas is due to the collision of its particles. Again, this 
theory requires us to suppose that the particles of one sort 
of gas require more velocity at the same temperature than 
the particles of another. According to the law of Avogadro, 
equal volumes of gases under the same condition of tempera- 
ture and pressure contain the same number of molecules. 
If we take two such equal volumes of oxygen and hydrogen, 
the volume of oxygen is found to weigh sixteen times as 
much as the volume of hydrogen. Calling the weight of 
the hydrogen atom one, that of the oxygen atom is sixteen. 
How can we explain the elasticity of these gases then upon 



50 A THEORY OF GSAVITATION, 

the impact theory of heat/ unless we assume that an atom of 
hydrogen acquires sixteen times the velocity of an atom of 
oxygen under the same temperature ? for the expansion of 
the gas would be in proportion to the momentum of its 
particles. The question, why there should be more latent 
heat in gases of small particles than in gases of large particles, 
and why the latter become saturated with heat and arrive 
at an equal temperature before the former, is generally 
explained by the assumption that all atoms, both large and 
small, have the same capacity for heat. This capacity must 
be construed to mean momentumhj theimpact-theorist; but 
I shall construe it to mean velocity, because the view which 
I have taken of heat recognizes the action of both forces, 
attraction and repulsion, at the same time. 

Assuming, then, that the particles of matter have a 
rotatory motion, and that heat is communicated from one 
to another by radiation through the interstellar medium, the 
meaning of the term S2)ecific heat may be thus illustrated. 
If oxygen and hydrogen be subjected to the same tempera- 
ture for any length of time, the atoms of oxygen acquire the 
same velocity as the atoms of hydrogen. But in the same 
weight of the two gases, the hydrogen molecules are sixteen 
times as numerous as the molecules of oxygen ; therefore 
taking a pound of each gas, the specific heat of hydrogen 
is sixteen times that of oxygen. According to the impact 
theory, the relation between the weights and specific heats 
of atoms is explained on the assumption that the atoms of 
gases are entirely free and acted upon only by heat ; and, 
therefore, an atom or molecule of hydrogen must move with 
sixteen times the velocity of an atom of oxygen in order to 
overcome the same pressure. I have already expressed my 
dissatisfaction with this hypothesis. For why should an 
atom of oxygen, when submitted to the same temperature 
for an indefinite length of time, acquire only one-sixteenth 



HEAT AND ELECTRICITY. 51 

the velocity of hydrogen ? By admitting the action of attrac- 
tion between the particles, I explain the capacity for heat of 
the two gases differently. For I suppose that the gravity of 
the particles of oxygen for each other is sixteen times as great 
as the gravity of the particles of hydrogen, and that, there- 
fore, sixteen times as much momentum in the case of oxygen 
is necessary in order to put its particles in the same rela- 
tion to one another as those of hydrogen. Then when the 
particles have this relation to one another, if we double the 
motion of these particles we double the temperature and the 
expansive energy of the gas. This explains why multiplying 
the specific heat of different substances in the state of gas 
by their atomic weights produces equal results. Now this 
law of equality of products holds good not only for gases, 
where we might have supposed the particles absolutely free 
from the influence of one another's attraction, but it holds 
good for solids, too, where we know the particles are not 
free from attraction ; and the view which I have taken of 
heat seems to explain the law for all three forms, and applies 
with the same simplicity to one as to another. 

The term ladiation is used to denote the passage offeree 
through the interstellar medium, and if in this way heat is 
communicated from one particle of matter to another, the 
particles of matter cannot be in contact, but must be 
separated by inter-spaces many times greater than the 
particles themselves. As these inter-spaces increase in 
magnitude, and the particles of any mass are removed 
farther and farther apart, the intensity of tbe radiation 
would vary inversely as the square of the distance between 
the particles, and, therefore, the conductivity of bodies would 
diminish with their expansion. Hence gases are worse 
conductors than liquids, and liquids are worse conductors 
than solids. It is true liquids are sometimes heavier than 
solids, which would seem to imply that their particles are 



52 A THEORY OF GRAVITATION, 

nearer together; but this is explained by the fact that solids 
have structure and liquids have not, so that the comparative 
lightness of the solid is due to its porous nature. Liquids 
and gases probably conduct equally well in all directions, 
but solids do not. This also is due to structure. If we 
examine the process of crystallization, we notice that the 
crystals are formed in long fibres, which lie parallel to one 
another. It is plain, from the law of radiation above stated, 
that the heat would be conducted best in the direction of 
these fibres. This is illustrated both in the melting of ice 
and the crystallization of snow. The formation of the "ice 
flowers" in the beautiful experiment of Tyndall maybe due 
to this cause, the ice in melting following the lines of its 
crystallization. 

The specific heat of bodies and their conductivity depend 
greatly on their physical condition. The same substance 
has not the same specific heat or the same conductivity for 
the solid, liquid, and gaseous form. Hence, in comparing 
substances with respect to their specific heats, they must be 
reduced to the same one or other of these three states. Gold 
as a solid cannot be compared with mercury as a liquid, but 
the mercury must be solidified; nor can hydrogen and 
oxygen, which cannot be solidified, enter the same table of 
specific heats with the metals. In comparing bodies in 
respect to their conductivity, we must have respect not only 
to their form, but also to their temperature. As their 
temperature increases their conducting power decreases. 
This may be due to the fact, that by the expansion of the 
conductor by heat the particles of it are moved farther from 
one another. In comparing the conductivity of solids and 
liquids where their expansion is little, it may not be so 
necessary to take their temperature into consideration; but 
it must be very essential in comparing that of gases, whose 
volume increases directly as their temperature when under 



HEAT AND ELECTRICITY. 53 

the same pressure. If the temperature of two volumes of 
gas under equal pressure is such that the temperature of one 
is twice that of the other, the bulk of one is also twice 
that of the other. In this condition the particles of one of 
the volumes are twice as distant from one another as the 
particles of the other. Applying the law of inverse squares, 
the conductivity of the more rarified gas would be in this 
case only one-fourth that of the denser gas. But if the 
elasticity of gases is due to the collisions of their particles, 
it does not appear, why, under the same pressure, a rarified 
volume of gas should be a worse conductor than one whose 
particles are closer together. 

It may be easier to imagine how a rectilineal vibratory 
motion of the interstellar medium may cause the vibrations 
of the molecules of ponderable matter, than how it can 
cause a circular motion. Yet we have many examples of 
the interchange of circular and simple projectile motions in 
sensible masses. Water, for example, may give a circular 
motion to machinery in three ways — by its impulse, in the 
case of an undershot wheel; by its weight, in the case of an 
overshot wheel ; and, third, by reaction in a peculiarly 
arranged horizontal wheel. On the other hand, the motion 
of wheels or machinery may communicate a rectilineal 
motion to water. Thus we may compare the inter-action of 
the interstellar medium and molecules to that interchange 
of motion which takes place between water and water-wheels, 
and thus the mode of conversion of radiant heat into a cir- 
cular molecular motion may be faintly conjectured. It may 
be that the varying densities of ether and caloric around 
atoms and molecules produce refraction, and by this means, 
in some way, cause the force, which is communicated by 
radiation, to proceed around the atoms and molecules with 
a whirling motion, and impart, by friction, a rotatory motion 
to them through their atmospheres. The refraction of the 

5* 



54 A THEORY OF GKAVITATIOlSr 



heat force would depend upon the condition of the heat- 
bearing medium or caloric atmosphere aronnd the mole- 
cule ; but the friction by which the heat force is commu- 
nicated to the molecule must, in a great measure, depend 
upon the construction of the molecule and the roughness 
and smoothness of its surface. • 

Now, the condition of the molecular atmospheres has 
already been described. For I have explained that these 
atmospheres increase in density outwardly or from the 
atoms when they are in motion, and inwardly when at 
rest. But since we have supposed them always to be in 
motion, whether in the solid, liquid, or gaseous state of 
matter, we must suppose that the radiating medium, if this 
be caloric, is in the former condition in the neighborhood 
of atoms and molecules. Since an atom is a simple body, 
we are able to form an almost exact idea of the nature of 
this condition. For by direct reasoning, we may define the 
different effects produced by the rotating atom upon the 
caloric at different points of its surface. But a molecule 
being a compound body, the nature of its atmosphere must 
depend upon the positions of the atoms which compose it, 
and the refracting power of its atm.osphere must depend 
not only upon its own motions, but upon the motions of the 
atoms. There is, however, one general effect which may be 
described; for the caloric atmospheres of all atoms and 
molecules vary in density, since by this condition attraction 
and repulsion are produced. 

Owing to the unequal density, therefore, of these atmos- 
pheres, we suppose the heat force to be refracted in passing 
through them. But shall we suppose, that it is refracted 
to the molecules or from them? The answer to this 
question depends upon the medium assumed for the 
passage of the force; for^ in regard to density, the relations 
of ether and caloric are opposite, the one increasing in 



HEAT AND ELECTEICITY. 55 

density as the other diminishes. But since caloric is more 
nearly related to ponderable matter than ether, it must 
from its nature be the medium of force, either heating or 
chemical, or both. In observing the passage of the heating 
and chemical rays through transparent bodies, we see that 
the heating ray is less refracted than the chemical ray. 
Ifow, the medium of the two rays may be the same. But 
if there is a separate medium for each, it is plain from this 
difference of refraction that the medium of the heat ray is 
the one which is more nearly related in its nature to 
ponderable matter. Let it be granted, therefore, that caloric 
is the medium of heat force, and we may proceed to answer 
the above question. 

From the fact, that heat and light in passing through 
diathermic and translucent bodies, like gas or water or glass, 
are more refracted in proportion to- the density of such 
bodieSj we might suppose, that the law of refraction would 
be the same through the imponderable medium, and that 
the heat force would be refracted from the molecules, 
because their atmospheres increase in density from them. 
But the cases are not analogous. For the particles of glass, 
gas and water are not truly the vehicles of the heat force, 
but this force is transmitted through the imponderable 
medium ; and if it is refracted more in water, than in air, 
it is because the latter presents less obstruction. The 
particles of ponderable matter are, however, the vehicles of 
sound, and stand in the same relation to sound as the caloric 
stands to the radiation of heat; that is to say, the vehicle 
of sound is ponderable matter, and the vehicle of radiant 
heat is imponderable matter. We must look, therefore, for 
the same relations to govern the refraction of heat in 
imponderable matter, which govern the refraction of sound 
in ponderable matter. Sound travels through air at the rate 
of one thousand and ninety feet in a second ; and through 



56 A THEORY OF GEAVITATION 



water four times, and through iron ten times as fast as 
through air ; and, generally, the rapidity of sound varies with 
the elasticity and density of the medium as in the case of 
air, water and iron. If sound, then, increases, with the 
density of the medium, through which it is conveyed, we 
may suppose, that the rapidity also of the heat force, in 
travelling through its proper medium, Avould increase with 
the density of the caloric. Hence in passing through the 
caloric atmospheres of atoms and molecules, the heat force 
would be refracted to these bodies and not from them ; and 
I suppose, that the meeting of the refractel forces in the 
proximity of the atoms or molecules might in some way 
whirl or eddy around them^ and impart in this way a circular 
motion. 

We have thus formed some idea of the mode, in which the 
heat force may be communicated through the interstellar 
medium, from one rotating particle to another. But we 
may well suppose, that the passage of radiation through 
ponderable matter is not always accompaaied with a conver- 
sion of the rectilineal motion of the interstellar medium 
into the circular motion of ponderable molecules. Some- 
times the ponderable molecules are simply agitated, and take 
the same kind of oscillatory motion as the interstellar 
medium. 

This is the case when bodies have the properties of trans- 
parency and diathermancy. They transmit the heat 
through them without being heated, or rendered luminous. 
They are not heated or luminous, because their motion is 
of the same character as radiant heat; but they refract 
because they do not move so readily. In order that a body 
may be visible it must resist the vibrations of the inter- 
stellar medium by reflection so as to give a character to 
them corresponding to each point on its surface. Hence 
transparent bodies, which give no character to these vibra- 



HEAT AND ELECTRICITY. 57 

tioiis but take the same motion as light, are invisible. Now 
if this reasoning is good to account for the invisible nature 
of transparent bodies, that their motion is vibratory like 
that of light, it must hold good conversely, that bodies which 
are heated by radiation and become visible, must at the same 
time take a motion different from that of light; that is to 
say, in the case of such bodies, the vibratory motion of 
radiant heat is transformed into a rotatory motion, other- 
wise the motion would pass through them and render 
them transparent. 

The waves of the interstellar medium, which produce 
white light, are not all of the same length, but decrease 
in magnitude from the red to the violet. Can this be 
explained by the assumption that the motion of molecules 
is vibratory? Can we suppose, that a molecule becoming 
luminous can vibrate in so many different ways as to pro- 
duce all the rays of the solar spectrum at once from the 
red to the violet, and even beyond the red on one side and 
the violet on the other ? If this question is to be answered 
in the affirmative, then we have to assume that each ray of 
the solar spectrum is the product of a different molecule or 
atom in the luminous body. For it would seem that as 
each string of a musical instrument has its own note, so each 
vibrating molecule must emit its own peculiar ray. Each 
luminous body, therefore, must be a more complex arrange- 
ment than the musical instrument, having as many different 
sorts of molecules or atoms as it emits rays. How does such 
a hypothesis then comport with the theory of atoms, where 
all the atoms of a simple substance such as carbon, which 
emits a white light, are represented as having the same 
weight ? Neither does this hypothesis explain why those 
atoms or molecules which produce the red rays should be 
set in motion first, or those which produce the violet, last. 

Let us consider then, on the other hand, how and in what 



68 A THEORY OF GRAVITATION, 

order the waves of light may be produced by a rotating 
molecule. This action of the molecule on the interstellar 
medium may be compared to the action of a water-wheel, 
composed of paddles of unequal lengths. The waves of 
water would correspond in magnitude, perhaps, with the 
length of the paddles, those * paddles stirring the water 
deepest producing the greatest waves, but the frequency of 
the waves depending on the rapidity of the wheel's rotation. 
So with the rotating molecule. For the aggregation of 
atoms in forming a molecule would give it a rough surface, 
corresponding to the paddles of the water-wheel. This 
surface, as the molecule rotates with rapidity, produces 
waves of light, varying in length with the distance of each 
component atom from the axis of the molecule. Now the 
atoms, which are most distant from the axis of the mole- 
cule, and which have therefore the longest range as the 
molecule rotates, are those atoms on its surface, which lie 
about its equator. These atoms, therefore, move with 
more rapidity and excite the ether waves with more frequency 
than atoms on other parts of the surface of the molecule, 
in what might be called its polar regions. Now the motion 
of the molecule upon its axis, might not be sufficiently 
rapid at first to effect the vibratory movement of the caloric, 
or ether, whichever we assume to be the medium of light; 
but in attaining the necessary velocity to produce light, it 
is plain, that the atoms in the equatorial part, would attain 
that velocity first. As the colors of the spectrum and the 
length of the ether waves depend upon the intervals of time 
when an atom leaves and returns to a point or when one 
atom arrives at a point vacated by another, it is plain, that 
as the rotatory motion of the molecule increases, a red band 
of light, as the molecule becomes luminous, would first 
encircle its equator, while all the rest of the molecule would 
be dark. But as the molecule further increases in motion, 



HEAT AND ELECTKICITY. 59 

SO that the dark portion becomes luminous, the red band 
of the equator gives place successively to a band of orange^ 
a band of yellow, and so on through the spectrum. If then 
we could see a molecule becoming luminous, we should first 
see a narrow band of red marking the equator of the mole- 
cule. This band would grow wider and wider, and would 
presently be divided in the center by a band of orange ; then 
a band of yellow would divide the orange, and this process 
would continue until a spectrum would appear on each 
side of the molecule, with the red ray nearest to the pole 
and the violet nearest to the equator. Here, then, is an 
argument drawn from the properties of visible heat in favor 
of the rotatory motion of molecules ; for in the order here 
mentioned, the colors of the spectrum are produced. 

A rotatory motion being assumed as that of the molecule 
of luminous matter in the production of light, we may 
proceed to explain the cause of its polarization. We know, 
that cold solid bodies as a rule are opaque, and that gases 
are invisible. It seems to be .in passing through the inter- 
mediate stage between the gas and the solid, that bodies 
become luminous. Sometimes, this transition is slow, 
and fusion or liquidity becomes one of the fixed states, as 
is the case with metals, many of which arrive at the liquid 
state immediately after they attain a white heat; sometimes 
it is instantaneous, as is the case with carbon. But in most 
cases those bodies, which require the highest temperature 
to produce the transition, emit the most brilliant light ; 
while on the other hand, those bodies which are capable of 
assuming the liquid or gaseous state at very low tempera- 
tures as a rule emit no light at all. These characteristics 
of luminous and non-luminous bodies here pointed out, as 
far as they hold good, are probably due in part to the 
velocity of molecules and partly to their shape. Take water 
as an example. This w^e know is incapable of producing 



60 A THEORY OF GRAVITATION, 

light either in its solid, liquid or vapor state. Now we 
think we have some id^a of the constitution of the water 
molecule. It is supposed to consist of one atom of oxygen 
and two of hydrogen. A molecule of this structure would 
be incompetent to produce all the ether waves of white 
light, and, according to our assumption, it Avould only be 
competent to produce two. Yet these molecules at different 
temperatures as happens in the atmosphere Avould be 
capable of absorbing rays of different magnitudes. But 
owing to the low temperature at which water passes into 
the liquid state, the motions of its molecules would be too 
slow to vibrate the ether at all. But a platinum or carbon 
molecule capable of emitting a white light, must be com- 
posed of many atoms. I have said, that it seems to be a 
rule, that bodies become luminous at the transition stage 
from solid to gas, that is to say, Avhen the molecules of bodies 
are in that position which is assumed in the liquid state. 
Let us suppose then, that we could see two luminous mole- 
cules of carbon, A and B, in this state. They would each 
appear to us to be striped with bands of color, running 
around the molecule parallel to its equator ; but the bands 
of color on the molecule A would be at right angles to the 
bands on the molecule B, because the two molecules are 
assumed to be in the liquid state, having their axis at right 
angles. This seems to me to illustrate, if not to explain, 
the '' two sides " or " right and left handedness " of a ray of 
light, the rays from B being at right angles to the rays 
coming from A. Hence the rays from one of these mole- 
cules might pass freely through a medium, which would 
exclude all the rays from the other, and vice versa. The 
2)olarization of the light, then, consists in presenting a 
medium in such a position as to reflect the rays from one 
molecule, and to refract those from the other. 
Now as to the difference of chemical and luminous rays 



HEAT AND ELECTRICITY. 61 

on the one hand, and radiant heat on the other, I am 
inclined to attribute them to widely different agents. The 
former I attribute to the oscillations of ether produced by 
the motions of atoms from place to place ; the latter to the 
undulation of caloric. It is a somewhat vague idea of this 
sort, which has led me to apply the term ether to one fluid 
of the double medium, and caloric to the other. For it 
is a very noticeable fact, that although light and radiant 
heat usually accompany each other, the quantities of each 
emitted by different bodies are by no means proportional, 
and sometimes one is emitted without the other. Vision 
may not be a fair criterion ; but the chemical effects of one 
class of rays seem to associate it with atoms, while the 
heating effects of the other class connect it with molecules. 
I am inclined to think, that chemical action takes place by 
the oscillation of ether, which does not, like caloric, impart 
motion to molecules of a rotatory character, but shakes the 
atoms together and changes their positions in molecules, 
just as nitro-glycerine is exploded by concussion. Light 
also by chemical action produces explosion. We may explain 
the difference in the causes of the heating and chemical 
effects, by the supposition that a body is heated, when the 
vibratory motion of the interstellar medium is converted 
into a rotatory motion of molecules ; and that a body is 
chemically effected, when no such convei'sion takes place, 
but the molecules receive an oscillatory motion, which being 
of a less regular nature than a rotatory motion, would tend 
to bring the atoms of one molecule under the influence of 
those of another. 



62 A THEORY OF GRAVITATION, 



CHAPTER V. 

ELECTRICITY EXPLAINED ON THE DOUBLE ETHER HYPOTHESIS, THE 
BASIS OF THE PRECEDING THEORY OF GRAVITY AND HEAT. 

In" the conduction of heat two bodies are cjncerned, the 
heated body and the cold body. In the conduction of 
electricity the two bodies concerned are the positive body, 
charged with positive electricity, and the negative body, 
charged with negative electricity. In both classes of 
phenomena the same fluids and the same kinds of motion 
occur, so that heat is sometimes converted into electricity 
and electricity into heat. 

If two masses of the same kind of matter be brought 
in contact, the one heated and the other cold, the cold body 
will absorb double ether from the heated body, until their 
bulks or volumes bear the same ratio to their Tespective 
weights. They will then be at the same temperature ; for 
neither will then have more tendency than the other to 
impart the fluid or to radiate force. But we may suppose 
the two bodies brought in contact to be of diflerent kinds, 
as one of zinc and the other of copper. These metals differ 
in the following respects : We observe that copper is a more 
compact metal than zinc. Its particles lie closer together. 
Although its atoms are smaller than those of zinc, it requires 
less heat to raise it to the same temperature, and in passing 
through one degree its expansion is much less. As a con- 
conductor it stands in relation to the other metal as three 
to one. Let us suppose, that the specific heats of the two 
metals have regaid to their molecular motions. The zinc, 
then, requires more molecular motion to raise it one degree 



HEAT AND ELECTEICITY. 63 

of temperature than the copper ; its interior work, there- 
fore, to use an expression of TyndaiPs, must be greater. 
Let us see what this is. In the first place it expands more 
than the copper, and absorbs more double ether in passing 
through one degree of temperature; and, secondly, being a 
much inferior conductor to copper, it draws its supply of 
caloric less readily. Hence we may infer, that both metals 
being heated to the same temperature, and placed under 
circumstances equally favorable for acquiring caloric, the 
better conductor or copper would acquire more caloric than 
the zinc in proportion to the amount of ether acquired. 
On the contrary, zinc, at the same temperature, has acquired 
more molecular motion, and its specific heat is greater than 
the copper's. Hence if we consider two insulated plates of 
copper and zinc at the same temperature, the zinc has the 
more molecular motion, and the copper a denser caloric 
atmosphere or more positive electricity. On account of the 
caloric being rarer in the zinc, than in the copper, the mole- 
cular motion of the zinc to sustain the same temperature as 
the copper must exceed that of the copper in the same 
proportion as the density of the caloric atmospheres of the 
copper molecules exceed those of the zinc molecules. Such 
then would be the relations of two insulated plates of zinc 
and copper, Avhile their conditions are dependent on the 
continual fiuctuations of temperature in surrounding media, 
either air or some other non-conductor. But if we bring 
them in contact these relations are changed and their 
electrical equilibrium disturbed. For the two metals in 
contact do not acquire and lose force and fluid according to 
the same law as when they are insulated, and when brought 
in contact the copper will be positive to the zinc. 

Electricity consists in disturbing the equilibrium between 
the two fluids, so that one body gets an excess of caloric and 
the other body gets an excess of ether. Hence no expan- 



64 A THEORY OF GRAVITATION, 

sion or contraction occurs if the two bodies so vary in their 
molecular motions as to always maintain the same amount 
of the mixed fluid though the proportions of the mixture 
vary. The body, which has a tendency to impart caloric is 
positive, and the body which has a tendency to impart ether 
is negative. It is not necessary, that the positive body 
should have more caloric or the ne2:ative more ether than 
the body in the opposite electrical condition. What con- 
stitutes its positive or negative condition is the tendency to 
impart the one or the other fluid. While no such tendency 
exists they are in electrical equilibrium. The insulated 
plates of copper and zinc were in electrical equilibrium. We 
bring them in contact and it is disturbed ; but it is restored 
again, when a sufficient quantity of the opposite fluids has 
been interchanged by the two metals. But until the 
equilibrium is restored, the copper is positive to the zinc and 
the zinc negative to the copper. Ether and caloric flow in 
opposite directions. The zinc derives caloric from the 
copper, and the copper derives molecular force and ether 
from the zinc. But when w^e again separate the two plates 
the electrical equilibrium is again disturbed, and the zinc 
will be found to be positive and the copper negative. How 
are we to explain this ? Positive electricity or caloric must 
have passed out of the copper into the zinc, and negative 
electricity must have passed out of the zinc into the copper, 
when they were in contact. And since no expansion of the 
zinc has occurred, and no contraction of the copper, the 
molecular motion of the zinc must have diminished and the 
molecular motion of the copper increased by the contact. 
After they are separated, however, the opposite electricities 
have a tendency to pass back again into their former condi- 
tions. The zinc molecule again assumes its velocity and 
expels caloric; the copper absorbs caloric and radiates its 
molecular force. The zinc has become positive, and the 



HEAT AND ELECTRICITY. 65 

copper negative. Hence it appears, that it is not an 
absolute excess of positive electricity or caloric, that renders 
one body positive and another negative; for the negative 
body may have more positive electricity than the positive 
body. For without regard to the quantity of electricity of 
either kind in either body, the mere separation of the two 
metals, or the bringing of them in contact, renders that 
negative, which before was positive, and visa versa. The 
question is w^iy contact and separation produces change in 
the electrical condition. 

I have shown, that heat is not to be explained by the 
supposition of force or fluid alone. It is thus also with 
electrical phenomena: the equilibrium of the fluids, and 
the disturbance of this equilibrium depend in a great 
measure upon the movements of the molecules of the 
electrified body. There is always a certain correspondence 
between the motions of molecules and their atmospheres. 
Increase their motions, the mass expands and the impon- 
derable fluids are absorbed; decrease their motions, the mass 
contracts and the fluids are expelled. When, in accordance 
with this correspondence, two contiguous bodies neither 
absorb nor impart caloric and ether, they have the same 
temperature. Capacity for heat is a term which denotes 
that some bodies arrive more readily at the same tempera- 
ture than others ; and that amount of force, Avhich compared 
with a standard, is necessary to raise the temperature of 
any substance through one degree is called its specific heat. 
The difierent capacities of bodies for heat may be due to 
several causes. In the case of the permanent gases, where 
the atomic motions are presumed not to vary and their 
positions in the molecules to be the same, each gas molecule 
being composed of two atoms, I have supposed the diff*erent 
speciOc heats to be due to a differenoe in chemical impulsion 
between the atoms. For the atomic and molecular motions 

6* 



66 A THEORY OF GRAVITATION, 

and positions being the same, and the conductivity of the 
gases equal, there appears to be no cause but the difference 
of atomic weight or chemical impulsion to prevent the 
heavy gases from expanding equally with the light. In the 
case of solid bodies on the other hand, as copper and zinc 
for instance, there is a difference in specific gravity, which 
does not accord with their atomic weights; and a difference 
in the positions of atoms in the molecules, so that the same 
molecular motion in the zinc produces more expansion than 
in the copper. The molecule of zinc being, therefore, less 
compact than the molecule of copper, may acquire and lose 
motion more readily. The greatest velocity which a mole- 
cule can have, I am inclined to think, is equal to the velocity 
of radiant heat. All space is filled with these radiations, 
moving with the same velocity in all directions, and 
imparting motion to molecules ; but owing to the different 
positions and conditions of these, some acquire more than 
others under similar circumstances, and lose more readily, in 
turn, that which they acquire. But besides the mode of 
acquiring molecular motion by radiation from distant and 
separate bodies, it is also acquired by contact. The property 
of acquiring it in these two ways may vary in different 
bodies. One sort of matter may excel another in losing and 
acquiring heat force by radiation; another may excel in 
communicating molecular motion by contact. Hence it 
may be that the electrical equilibrium of copper and zinc 
is destroyed by bringing the metals in contact and separating 
them again, thus constantly changing the motion of the 
molecules upon which the equilibrium depends. The passage 
of ether and caloric from one body to another in opposite 
directions for the purpose of restoring equilibrium, or estab- 
lishing those relations between molecular forces and mole- 
cular atmospheres, which certain conditions require, is what 
constitutes an electric current. The conduction of electricity 



HEAT AND ELECTRICITY. 67 

is effected much more rapidly than the conduction of heat, 
because no expansion occurs, and less interior work is done. 
But when the conductor resists the passage of the current, 
electricity is converted into heat. 

The conduction of heat is the passage of the two ethers in 
their mixed condition through the conductor, both fluids 
moving in the same direction. A current of electricity, on 
the other hand, consists of the passage of the same fluids, but 
in opposite directions and in equal amounts. When heat 
passes, therefore, the body from which it passes is diminished 
in bulk and the heated body is increased. The contraction 
and expansion are not always equal, however, in the two 
bodies, which shows, that it is the heat force, and not the 
heat fluid, which always remains a constant quantity; the 
latter being mainly the medium through which the effect of 
the former is produced. But when electricity passes from 
one body to another, neither body is expanded or contracted, 
because each receives as much of one kind of fluid, as it 
discharges of another. "An electric current," says Faraday, 
"in circulating through a thick or thin wire, exhibits the 
same deportment as a fluid flowing through a wide or narrow 
tube." As a given quantity of fluid requires more time or 
greater pressure to pass through a narrow tube than through 
a large, so a thin wire offers a greater resistance than a thick 
one to the passage of a current of electricity. The current 
is thus retarded and diminished, one portion only passing 
through the conductor, the other being converted into heat. 
This is an example of the conversion of electricity into heat. 
The heating effect is probably produced by the accumulation 
and combination of the two fluids in the heated body, 
instead of continuing onward in their opposite directions to 
the bodies oppositely electrified. 

Instances of the conversion of heat into electricity also 
occur. One of the most obvious of these is that which occurs 



68 A THEORY OF GRAVITATION, 

in the thermo-electric pile. Thermo-electricity probably 
consists in the separation of the double ether into its two 
components. The thermo-electric pile is formed by the 
junction of two metalic bars, one of antimony and the other 
of bismuth, welded together at one extremity of each and 
having the two other extremities free. Upon heating the 
point where the two metals are joined, and connecting the 
two free ends by a piece of wire, an electric current is 
generated, the direction of which is from bismuth to ant*- 
mony across the junction, and from antimony to bismuth 
through the connecting wire. The currents flow in the 
opposite direction, when the pile is cooled. From the 
combination of almost any other two metals, thermo-electricity 
may be obtained, but the current is most readily produced 
by that of antimony and bismuth. 

The generation of thermo-electricity seems to me to be 
based on the same principles as the generation of electricity 
by contact, as occurs between the plates of copper and zinc. 
These principles were explained as, first, the fluctuations of 
temperature ; and, second, the dissimilarity of molecular 
structure, which causes one metal to be more susceptible to 
heat force under one condition, and another metal under 
another condition. Eadiation was supposed to be the motive 
force operating upon the insulated plates of zinc and copper, 
and the zinc molecules were supposed to receive more motion 
in this way than the copper; but when the two metals are 
brought in contact, the zinc molecules part with motion to 
the copper molecules and receive positive electricity, and the 
copper molecules acquire motion and negative electricity. 
In the thermo-electric pile the bismuth stands in the same 
relation to the antimony as the copper to the zinc in the case 
above mentioned. To tiie external source of heat antimony 
has a nearer relation and acquires and loses the heat force 
more readily than the bismuth, and acts, therefore, as a 



HEAT AND ELECTKICITY. 69 

medium between the two others. Hence in heating the pile 
the bismuth receives molecular force from the antimony and 
gives off caloric or positive electricity; and in cooling the 
pile the bismuth gives back the heat force and the electric 
current is reversed. But through the connecting wire, when 
the pile is heated, the caloric or positive electricity passes 
from the antimony to the bismuth, because the antimony 
while receiving heat force more readily at the juncture than 
the bismuth, loses it in turn more rapidly at the free end of 
tlie bar. The relations, therefore, of the two metal bars at 
their extremities Avould be reversed. The free ends bear the 
same relation to each other while the pile is heating, as the 
joined ends ^vould bear when the pile is cooling. Thus I 
explain the production of thermo-electricity. It is the 
decomposition of heat fluid or double ether. The two fluids 
separate at the juncture of the bars, and become positive and 
negative electricity. As the temperature at the junction is 
raised, the current flows ; when the temperature is stationary, 
it ceases; w^hen tlie temparature is lowered, it flows again, 
but in the opposite direction. 

Heat and electricity may be produced by chemical action 
or affinity, and by mechanical force or friction. Electricity 
produced in either of these ways, may be explained as in the 
case of that produced by the thermo-electric pile. It is the 
decomposition of fluid heat into currents of caloric and 
ether, the heat being converted into electricity as soon as 
formed or collected. 

Let us first inquire how electricity is produced by chemical 
action. If two plates of metal, one of zinc and the other of 
copper, be im^mersed in water or dilute acid and then be 
brought in contact, either immediately or mediately by 
means of a conducting wire, it will be found, that as long as 
the two metals remain in contact, there will be a constant 
current of positive electricity circulating from the zinc 



70 A THEORY OF GRAVITATION 



through the water or dilute acid to the copper, and from the 
copper through the point of contact or connecting wire of 
the two metals to the zinc; and on the other hand, that a 
similar constant current of negative electricity will be 
traversing the circuit described, in an opposite direction. 
The combination above described constitutes what is called 
a simple voltaic circle. 

The chemical action which takes place between the water 
or acid and the metal liberates heat force ; for less heat 
force is required to sustain matter at the same temperature 
in some conditions than in others. Let it be granted then, 
that the water and metal enter into the condition of a new 
compound, and that heat force is liberated. This heat force 
then produces expansion and the consequent absorption of 
double ether at the point of contact of the water and the 
metal, where the new compound is formed. It is found, 
that the zinc is more acted on by the water or acid than the 
copper; it therefore acquires by the chemical action more 
heat force than the copper, and stands in the same relation 
to the copper as the antimony was supposed to bear to the 
bismuth in the thermo-electric pile. It also bears the same 
relation to the copper, as it was supposed to bear when two 
insulated plates, one of copper and the other of zinc, are 
brought in contact. In both cases the zinc parts with mole- 
cular force to the copper, and the copper transmits positive 
electricity to the zinc. In both cases heat is converted into 
electricity. In one case the heat was supposed to be derived 
by radiation or contact with the insulating medium ; in the 
other case the source of heat is supposed to be chemical 
affinity. 

Heat and electricity are generated by friction. In elec- 
trization by this method, we may suppose, that the mechanical 
force is first converted into heat, and this again converted 
as readily as made into electricity by contact, as was the case 



HEAT AND ELECTRICITY. 71 

between the copper and the zinc. We know, that one kind 
of electricity is never produced without the other, and that 
they are invariably produced in equal quantities. '*When 
one insulator is rubbed against another, one of them becomes 
charged w4th positive and the other with negative electricity ; 
and with any given pair of materials, one invariably becomes 
positively electrified and the other negatively; but whereas 
glass rubbed with silk or flannel becomes positively 
electrified, when rubbed with cat's skin it becomes negatively 
electrified. It follows from this that the positive or negative 
electrization of the material does not depend absolutely on 
the substance of that material, but depends on some peculiar 
relation between the two substances in contacts This 
relation may be the same as I supposed to exist between the 
copper and the zinc, or between the bismuth and the anti- 
mony. The heating effect produced by friction imparts 
more molecular motion to one non-conductor than to the 
other non-conductor. The latter corresponds to the copper, 
the former to the zinc. Eesinous substances rubbed with a 
dry silk cloth become negative; glass similarly rubbed 
becomes positive. While the rubbing continues, the 
resinous substance is positive to the silk, and the glass is 
negative to the silk ; but when the friction is discontinued 
and the bodies are separated the electrical condition of the 
non-conductors is found to be reversed. Hence we may 
infer from the explanation I have already given of electricity, 
that the molecules of the resinous substances correspond to 
those of copper or bismuth, and acquire motion less rapidly 
than the molecules of the silk; and that the silk molecules 
on the other hand correspond to the molecules of the zinc or 
antimony. Hence in contact the positive electricity flows 
from the resinous substance to the silk, just as in the thermo- 
electric pile it is found to flow across the junction from the 
bismuth to the antimony, and the negative electricity flows 



72 A THEOEY OF GKAVITATION, 

in the opposite direction from the silk to the resinous 
substance. But when the resinous substance and silk are 
separated after having been rubbed together, the resinous 
substance will be negative, and the silk rubber will be 
positive, as was the case with the copper and the zinc after 
being brought in contact and separated. The molecules of 
glass stand in the opposite relation to the molecules of silk, 
or as the zinc to the copper. The glass acquires molecular 
motion by friction more rapidly than the silk, and, therefore, 
absorbs caloric and parts with ether. Thus the glass and 
resinous substance are oppositely electrified, because their 
molecules stand in opposite relations to the molecules of silk 
in regard to the quality of receiving motion from friction. 

A hot body rubbed by a cold one identical with it in 
chemical composition becomes negatively electrified. Again, 
when two pieces of glass are rubbed so that all the parts of 
one pass over one part of the other, the former is positive and 
the latter negative. It is evident that by rubbing two pieces 
of glass together in this manner one would become more 
heated than the other; so that I will consider this as only 
another example of a hot body rubbed by a cold. To make 
this example of electrization similar to the others, we must 
suppose that the molecules of the cold body acquire motion 
by the friction more rapidly than the molecules of the hot 
body, and that they part with some of the motion thus 
acquired to the hot body; that this communication of motion 
from the cold to the hot body is not such as to increase the 
temperature of the hot body, but such only as to retard the 
cooling of the hot body in contact with the cold body. If 
this be true the electrization effected in this way falls under 
the same law of relation as that supposed to exist between 
the zinc and the copper, the antimony and the bismuth, the 
glass and the resin. 

I have now defined electricity, as I described heat, as the 



HEAT AND ELECTRICITY. 73 

joint product of fluid and force. I will use the term conduce 
tion to denote the passage of the fluids, and the term induction 
to denote the passage of electric force. Kadiation is the 
passage of force by a vibratory motion through the inter- 
stellar medium ; induction takes place by the intervention of 
ponderable matter. To illustrate by the insulated plates of 
copper and zinc, I supposed them both to be heated by 
radiation, and that the zinc molecules received more mole- 
cular motion in the same time by radiation, than the copper, 
and that drawing caloric from the same source as the copper, 
and being at the same time a worse conductor, it had an 
inadequate supply. When, then, it came in contact with the 
copper, it parted with molecular motion by induction and 
received caloric or positive electricity by conduction. An 
electric discharged the passage both of fluid and force. 

"Attenuated gases," says Grove, " may be regarded in one 
sense as non-conductors, in another as conductors; thus if 
gold leaves be made to diverge by electrical repulsion, in air 
at ordinary pressure, they in a short time collapse, while in 
highly rarified air, or what is commonly termed a vacuum, 
they remain divergent for days; and yet electricity of a 
certain degree of tension passes readily across attenuated air 
and with difficulty across air of ordinary density." This 
passage from Grove's essay on "Correlation of Physical 
Forces," contains facts, which appear to me to be unex- 
plainable upon the assumption that electricity consists of 
fluid alone or force alone. But they may be explained upon 
the assumption that electrical phenomena are the joint 
result of fluid and force. Upon this assumption the facts 
above mentioned may be thus accounted for: discharge 
never takes place without induction. Where the two elec- 
trified bodies are separated by a vacuum no induction can 
occur; for the passage of force by induction requires the 
intervention of ponderable matter, and consequently there is 



74 A THEORY OF GRAVITATION, 

no discharge. Where, on the other hand, neither of the 
electrified bodies is placed within the vacuum, they have a 
channel of communication between them for the electric 
force through the intervention of ponderable matter, which 
may be the air surrounding them. Through this medium 
then the electric force may pass by induction, while the 
electric fluid passes without obstruction through the vacuum, 
" It is frequently said, that positive electricity attracts 
negative electricity, but that positive repels positive, and 
negative repels negative. We have stated, that electrified 
bodies do present attractions and repulsions of this kind, 
and by a slight extension of language the electricity itself 
may be spoken of as attracting or repelling; but there is a 
further phenomenon called statical iJiduction, which does 
appear more distinctly to represent an attraction or repulsion 
of electricity, besides the attraction and repulsion of the 
bodies charged with electricity. If a body, A, charged with 
positive electricity, be brought into the neighborhood of a 
body B, at a difl'erent potential it will attract negative 
electricity to that end of the body B, which is near it, and 
repel positive electricity to the remoter portions of B. If 
the body B be insulated, it neither loses nor gains electricity, 
but its ends are competent to produce electrical phenomena 
of opposite kinds. Separating the two ends we may retain 
each charged with its positive and negative electricity. Or 
if we connect the further end of B with the Earth even for 
a moment, the positive electricity will be driven off to the 
Earth, and a permanent negative charge will then be retained 
on B. Otherwise when A is removed the positive and 
negative electricity on B recombine and exactly neutralize 
one another. By induction, as in the case of electricity 
obtained by friction, precisely equal quantities of positive and 
negative electricities are simultaneously produced.'' I shall 
attempt to explain this phenomenon somewhat in the manner 



HEAT AND ELECTRICITY. 75 

in which I explained the electrization of the copper and 
zinc when brought in contact and afterwards separated. 
The body A, which is positively electrified, has less mole- 
cular motion than the body B, but a denser atmosphere of 
caloric around its molecules. A then corresponds to the 
insulated plate of copper, and B to the insulated plate of 
zinc. 

As soon, however, as the two bodies are brought near each 
other, the former acquires and the latter loses molecular 
motion upon their contiguous surfaces by induction. Perhaps 
the motion does not actually pass, unless a discharge of 
positive electricity passes, but that there exists only a 
tendency to pass, the actual passage of force being prevented 
by the insulator, which prevents the passage of the fluid 
electricity. The tendency to pass increases as the bodies are 
approached, and diminishes as the bodies are separated. 
But reasoning as if the passage of the force actually occurred, 
A will have more molecular force on its side next to B, than 
on the side opposite ; B, on the contrary, will have more on 
the side farthest from A than on the side next to A. Thus 
A acquires motion or a tendency to motion by induction 
from B, just as the piece of copper was supposed to acquire 
molecular force by contact with the zinc; and when again 
A is moved out of proximity with B, the two bodies are 
affected as the copper and zinc after separation ; for A loses 
the tendency to acquire force by induction, and B the 
tendency to impart. The insulator prevents the positive 
electricity from passing from A to B, and consequently the 
negative from passing in the opposite direction. But at the 
same time, owing to increased motion in the molecules of A 
and diminished motion in the molecules of B at their con- 
tiguous or adjacent sides, the surface of A next to B will 
have a tendency to discharge positive electricity, while in 
proximity with B, and the corresponding surface of B will 



76 A THEORY OF GRAVITATION, 

have ii tendency to discharge negative electricity while in 
proximity with A. Hence there are hvo modes of insulatio7i : 
first, by a vacuum, which prevents the passage of force by 
induction; second, by a non-conductor, which prevents the 
passage of fluid electricity. Let ns suppose a third body, C, 
to be so placed, that B shall be' in a position between A and 
C ; B will induce in a condition similar to that induced, in 
B by A. For if there is a tendency in A to abstract motion 
from Vj so as to reduce its molecular force to a condition 
below that of surrounding bodies, there must be a tendency 
in B to abstract molecular force from C to an equal amount 
Avith that which it imparts to A. Hence B acts as a con- 
ductor between A and 0, when all three bodies are brought 
in contact, and the fluids and force pass simultaneously. 

Thus far I have considered induction, only as it appears 
in static electricity, and which is called electrostatic induc- 
tion; induction also takes place between conductors 
through which currents are passing and. neighboring con- 
ductors, and is then designated electromagnetic induction. 
"This induction is the unfailing accompaniment of the 
beginning or increase and termination or decrease of a cur- 
rent, for there are always conductors somewhere near in 
which the induced currents flow. The induced currents 
diminish for the time being the strength of the inducing 
current, and thus we see, that neighboring bodies change 
the rate, at which a beginning or ceasing current comes to 
its permanent condition. If the whole or a large part of a 
circuit of small resistance is very near the inducing current 
and so disposed that the induction tends to occur throughout 
in one direction, the induced current will be considerable, 
and its reaction on the inducing current will also be great, 
shortening the time it requires to reach the permanent con- 
dition. If the circuit, in which the induced current flows, 
is on the contrary, far removed from the inducing current, 



HEAT AND ELECTRICITY. 77 

or only exposed to induction for a small part of its length, 
or so placed that the current tends to flow in opposite 
directions at different parts of the circuit, or has a great 
resistance, then the induced current will be small and its 
reaction on the inducing current will also be small. The 
inducing current produces an electromotive force iu the 
circuit conveying the induced current, and we may say that 
the induced^ current is due to the induced electromotive 
force." 

Let us suppose a current of positive electricity to be passing 
through a circuit A, B, C, etc., in the direction of the 
alphabet. This current will induce in a neighboring con- 
ductor, a^ h, c, a current of positive electricity which will 
flow against the alphabet. Electricity consists, as I have 
remarked, not only of the passage of fluids through the con- 
ductor, which is called conduction, but in the passage of 
electromotive force, which I have called induction. The 
conduction or passage of the fluids is caused by the induc- 
tion of the force. This I have already explained ; and we 
have only now to suppose, that the insulated bodies A, B, 
and C, which were supposed to be electrified, the first with 
positive electricity by friction, and the second and third by 
induction, have been brought in contact and form a con- 
ductor A, B, 0, through which a current of positive elec- 
tricity passes from A to C. According, then, to the expla- 
nation already given, the caloric or positive electricity flows 
in the direction of the alphabet through the conductor, and 
the electromotive force moves against the alphabet. The 
fluid passes from A to B and from B to C, only when these 
bodies are in contact, formiing a chain or channel, which is 
called a conductor. The force, however, Avas supposed to 
pass between them by induction, even while they were 
insulated. Now, as we supposed, that the electromotive 
force could pass and did pass from B to A and from C to B 



78 A THEORY OF GRAVITATION, 

by induction, while they were separated by insnlators, so 
we may suppose that the electromotive force may pass from 
the conductor A, B, C, D, etc., by induction to the neigh- 
boring conductor a^ i, c, d, etc. 

It is found by experiment, that when the conductors 
approach, or when the current in A, B, 0, D, commences or 
is increased, the induced current in a, i, c, d^ will move 
opposite or against the alphabet: but that when the 
inducing current in A, B, C, D, is removed from the con- 
ductor a, h, c, d, or is diminished or ceases, the induced cur- 
rent moves with the alphabet or in the same direction as 
the inducing current. In the former case when the inducing 
current is increasing, the electromotive force in the induced 
current moves from atoi and from d to c, and so on in the 
direction of the alphabet; but in the latter case, when the 
inducing current is diminishing, the electromotive force in 
the induced current moves against the alphabet. We are 
now to inquire, why the electromotive force in A, B, C, D, 
induces an electromotive force in a, J, c, cZ, which moves in 
one condition of the current in the same direction as the 
electromotive force in A, B, C, D, and in another condition 
of the inducing current in the opposite direction. 

For a current to flow from A to D, A must be at a higher 
potential or have more positive electricity; and according to 
bur theory there must be more electromotive force at D than 
at A. Now if we compare the conductors A, B, 0, D, and 
a, b, c, rf, which are supposed to be side by side, while a cur- 
rent is passing through A, B, C, D, in the direction of the 
alphabet, we shall find that there is more electromotive force 
at D than at c?, and less at A than at a, while the current is 
increasing in A, B, C, D. Hence the conductor A, B, C, D, 
will induce electromotive force from D into the conductor 
a, 5, c, d^ at the point d, which will begin to pass from d to 
a, and the point a will induce electromotive force into A. 



HEAT AND ELECTRICITY. 79 

Thus the presence of the conductor a, 5, c, d, in the neigh- 
borhood of the conductor A, B, G, D, will diminish the flow 
of electromotive force from D to A, through the conductor 
A, B, C, D, and will cause a passage of electromotive force 
from ^ to ^ in the conductor a, h, c, cl. Hence we see, since 
it is the flow of the electromotive force from D to A, which 
produces the flow of the fluid electricity from A to D, that 
the current of A, B, C, D, must be retarded by the induction 
of electromotive force in a^ I, c, d, at the point d from D, and 
in A, B, 0, D, at A from a. This induction will take place 
as long as there is a dissimilarity in the condition of the two 
conductors. As long as the inducing current increases and 
the force of electricity grows up in D more rapidly than in 
A, the current A, B, 0,0, will be resisted and retarded, and 
a current will be induced in a, b, c, d, in an opposite direc- 
tion to the inducing current. As long as the ratio of the 
electromotive force at D to that at A is greater than that of 
d to a, the point D will continue to induce force in d, and 
the point a will induce force in A, and the inducing and 
induced currents will flow in opposite directions. But as 
soon as this proportion is reversed, so that the ratio of d to a 
is greater than the ratio of D to A, which will occur when 
the inducing current decreases, the flow of the electromotive 
force in ^, 5, <?, d^ will also be reversed, so that A will induce 
electromotive force in a^ and d will induce it in D. Hence 
the neighboring conductor ^, 5, c, fZ, serves as a reservoir in 
which the electromotive force of A, B, C, D, is stored. The 
flow of the inducing and induced currents will then be in 
the same direction, and the diminution of the inducing cur- 
rent is retarded. Thus we see, that the effect of the 
conductor a, i, c, d, upon the conductor A, B, C, D, is to 
delay change in its electrical condition, since they react upon 
each other, having a tendency to induce the same relations 
between the extremities of the one, as subsists between the 



80 A THEORY OF GRAVITATION, 

extremities of the other. In the conductor a, Z>, c, d, I haye 
supposed the positive electricity to flow in the same direction 
as the electromotive force; for the fluid does not leave the 
conductor, but the induced electromotive force merely afifects 
its distribution, the fluid accumulating where the motion is 
diminished, and being rarified where the motion is increased. 
Otherwise the electricity would be converted into heat. But 
the conductor A, B, 0, D, serves merely as a conductor 
between two electrified bodies, and the fluid and force pass 
in opposite directions to restore the electrical equilibrium. 
The approach of the circuit A, B, C, D, to the conductor 
a, ?>, c, d, has the same effect as the increase of the inducing 
current, and the removal of the circuit as the diminution of 
the current. 

But besides the efi'ects, which the approach and removal 
of the circuits A, B, C, D and a, h, c, d have on the induc- 
ing and the induced currents, the phenomenon presents 
another feature, which is the resistance of the currents to 
the approach or removal of the circuits. Thus when we 
attempt to bring the circuits nearer to each other, we induce 
currents which move in opposite directions, and currents 
moving in opposite directions repel each other; and when 
we remove the circuits farther apart, we induce currents 
which move in the same direction, and currents, which 
move in the same direction, attract one another. The cause 
of the currents moving in the same direction under one con- 
dition, and in opposite directions under a change of this 
condition has been explained; we are now to explain the 
action of the currents on the movement of the conductors, 
or why it is that currents moving in the same direction 
attract, and moving in opposite directions repel one another. 
These attractions and repulsions are wholly distinct from 
the attractions and repulsions between charges of static elec- 
tricity. For in these the positive body or the positive pole 



HEAT AND ELECTRICITY. 81 

attracts the negative and repels the positive, so that likes 
repel likes and attract unlikes. But in the attractions and 
repulsions between currents of electricity, the positive parts 
of a circuit attract the positive parts of an adjacent circuit, 
and the negative attract negative, or else the negative and 
positive repel each other. 

Two parallel wires in which electric currents flow in the 
same direction attract one another; and two parallel wires 
in which electric currents flow in the opposite directions 
repel one another. It is usual to describe these phenomena 
as if there were an attraction between the electricity of one 
circuit and that of another. It is not likely, however, that 
the opposite electricities, which attract each other in the 
same conductor, should repel each other between neighbor- 
ing conductors. The most probable view to take is, that the 
phenomena are produced by the peculiar conditions in which 
the molecules of the conductor are thrown by the passage of 
the electricity, so that in one condition the impulsion of the 
molecules of one conductor for those of the other is increased, 
and in the other condition the property is reversed. Thus 
the two conductors stand in the same relation to each other 
as two molecules, which in the position of parallelism, rota- 
ting in opposite directions, repel one another and constitute 
the gaseous state of bodies, and rotatmg in the same direc- 
tion attract one another and constitute the solid form. These 
properties of electric currents^ discovered by Ampere, seem 
to have suggested the three positions of molecules in the 
three forms of matter. 

I have explained how in some positions of molecules, the 
same amount of rotary force may produce more repulsion, 
than in others. Now if a current of electricity passing 
through a wire would polarize all its molecules and cause 
them to rotate at right angles to the direction of the current 
as I have supposed, then the three positions of the circuits 



82 A THEORY OF GRAVITATION, 

corresponding to the three positions of molecules in the solid, 
liquid and gaseous forrns of matter, would produce analo- 
gous effects. For any two conductors can be so arranged as 
to place the molecules of one in any of these three positions 
with regard to the molecules of the other; and although no 
two molecules at so great distance apart as the two wires 
would produce any perceptable effect the one upon the other, 
yet in masses they might ; so that electrical repulsion bears 
the same I'elation to gravity, being action between masses, as 
heat bears to the cohesion of molecules. 

The readiness with which molecules of masses are polar- 
ized by the electric current in one direction may be that, 
which constitutes a good conductor. Hence we may imagine 
why solids, whose molecules rotate in the same direction, or 
nearly in the same direction, are generally good conductors. 
While liquids may be classed as imperfect conductors ; and 
gasses, in their ordinary state of density are non-conductors. 



HEAT AND ELECTRICITY. 83 



CHAPTER VI. 

ON MAGN E T IS M. 

Every current of electricity through a conductor is appar- 
ently accompanied by two modes of motion, one directly 
through the conductor, and the other, termed magnetism, in 
circles or spirals around it. Magnetic currents, as this spiral 
motion may be designated, are probably produced in the 
molecular atmospheres of the conductor by the rotation of 
the molecules. It is these which effect the attractions and 
repulsions between conductors, which I have already de- 
scribed, causing conductors through which currents are pass- 
ing in the same direction to attract, and conductors through 
which currents are passing in opposite directions to repel 
one another ; from which it happens, that two conductors, 
through which electric currents are passing tend to place 
themselves in parallel positions. This I have supposed to be 
due to the polarization of molecules, which are made to 
rotate at right angles to the direction of the currents. Hence 
an electric current is found to shorten a conductor as well 
as to make it more tenacious ; for the attractions of mole- 
cules for one another is strongest between their poles. 

But when a magnet is brought near a wire, through which 
a current of electricity passes, it is always deflected at right 
singles to the current. If now we attribute the deflection of 
the magnet and the parallelism of the two conductors to 
molecular forces, we shall have to conclude, that the mole- 
cules of the deflected magnet are polarized at right angles 
to the line of polarization of the molecules of the conductor. 
Hence the magnetization of a bar of iron is said to have an 
effect upon the texture of the metal unlike that produced by 



84: A THEORY OF GRAVITATION, 

the current of electricity upon the conductor. For the wire 
is made shorter and more tenacious by the passage of the 
electricity; but the bar is lengthened by being magnetized 
and is rendered more brittle. 

In a conductor, through which a current is passing, the 
arrangement of the molecules* may be compared to parallel 
rows of beads strung on straight wires ; the structure of a 
magnet may be compared to beads strung on a helix. If the 
above conductor be placed by the side of another conductor, 
it will induce a molecule arrangement in this conductor 
similar to its own. This sort of action of the electromotive 
force is essential to the induction of currents. Magnetiza- 
tion is produced by the induction of a current into a bar of 
iron or steel by winding the conductor, through which the 
current is passed, around the bar to be magnetized. The 
molecular arrangement of the bar then becomes like that 
of the coil of wire in which it is enclosed. Thus a simi- 
larity of structure gives rise to that similarity of action which 
subsists between a magnet and a coil, when the latter has a 
current passing through it. The opposite ends of the coil 
have the same properties as the opposite poles of a magnet, 
and if a coil be brought into the neighborhood of an electric 
current it will be deflected like a magnet. 

Let us examine then into the properties of the coil, with 
an electric current passing through it. The coil acts like a 
magnet and is capable of inducing magnetism. From what 
I have already said on the subject of electro-magnetic induc- 
tion, we may readily understand how a current would be 
induced into an unbroken circuit moved into the neighbor- 
hood of either pole of the coil, and when electricity is 
induced, the magnetic energies always accompany. The 
unbroken circuit may be either a bar of soft iron or it may 
be another coil. If we approach the solenoid, for such the 
inducing coil may be called, to the circuit or increase the 



HEAT AND ELECTRICITY. 85 

current in the solenoid, a current is induced in the circuit, 
which moves oppositely to that in the solenoid. The induced- 
current magnetizes the conductor, through which it circu- 
lates; and as long as it moves in an opposite direction to 
the inducing current the induced magnetism will be oppo- 
site to that of the solenoid, and the north pole of the sole- 
noid will induce a north pole in the circuit, and a south pole 
will induce a south pole. The circuit and solenoid then 
repel each other. But if we withdraw the solenoid or 
diminish the inducing current, a current is induced, in the 
circuit moving in the same direction as the inducing cur- 
rent. So long as the currents move in the same direction a 
north pole will induce a south pole, and a south pole a north 
pole. 

If we substitute for the circuit a bar of soft iron it will 
be magnetized and demagnetized in the same manner as a 
ring or coil. If it be a steel bar it may be permanently 
magnetized. Now a permanent magnet differs in some 
respects from a solenoid. In the first place, it has not cur- 
rents of electricity circulating through it, but it has mag- 
netic currents or magnetism, which is due to molecular 
forces. Nevertheless it is like the solenoid in inducing both 
electricity and magnetism ; for induction takes place between 
the molecules of insulated conductors, and not between the 
currents of electricity w^hich pass through them. It is more 
of a molecular, than an electrical phenomenon. We may 
suppose a bar of steel to have been magnetized by the sole- 
noid. We may then take the steel magnet, and substituting 
it for the solenoid, produce the same results upon a neigh- 
boring circuit. We may with the steel magnet, which has 
no electric currents circulating through it, induce electric 
currents and magnetism in the circuit. If we approach the 
circuit to the magnet, we induce a current of electricity in 
the circuit and a magnetism which produces repulsion. If 



86 A THEORY OF GRAVITATION 



we withdraw the circuit, we reverse the current and induce 
a magnetism which attracts. Varying this process a little, 
magnets may be made to induce magnetism, without inducing 
electric currents. We place the opposite poles of two 
equally strong magnets in the center of a bar to be magnet- 
ized, and by drawing them simultaneously away from the 
center to the two ends, produce an- effect corresponding to 
the withdrawal of the circuit from the magnet. The same 
principles apply to the following method of magnetizing a 
horse- shoe bar : I*lace the ends of the bar in contact with 
the poles of a horse-shoe magnet, then draw a bar of soft iron 
over the horse-shoe bar away from the poles of the magnet. 
This has the same effect as withdrawing the circuit, in the 
experiments mentioned above. 

It has been said, that currents moving in the same direc- 
tions attract one another, but moving in opposite directions 
repel. The principles, upon which these phenomena were 
explained, apply to the polar attractions and repulsions of 
solenoids and magnets. If two solenoids be applied with 
the north pole of the one to the north pole of the other, or 
with south pole to south pole, the currents oppose and pro- 
duce repulsion by giving to the molecules of the one that 
relative position to the molecules of the other, which 
according to hypothesis constitutes the gaseous form of 
matter. But if the north pole of one is applied to the south 
pole of the other, the currents move in the same direction 
and the molecules take the position for the solid form. If a 
solenoid is placed parallel with another solenoid, so that the 
poles of one are applied to the opposite poles of the other 
they attract, because the magnetic currents produced by the 
rotation of the molecules move along the surface of the 
solenoids in opposite directions. But if the position of the 
solenoids is reversed, so that the magnetic currents move in 
the same direction, the solenoids are repelled. For moving 



HEAT AND ELECTKICITY. 87 

in the same direction the magnetic currents assist each 
other; but moving in opposite directions, the effect is 
neutralized and the caloric atmospheres of the molecules 
are made more dense. For I will again repeat, that the 
attractions and repulsions between magnets, and the attrac- 
tions and repulsions between conductors, through which 
electric currents are passing, are all due to the same causes, 
and are of the same nature as the attractions and repulsions 
between molecules in constituting the solid, liquid and 
gaseous forms of matter. 

We may describe or distinguish the two unlike or oppo- 
site poles of a magnet as follows : The positive pole is that, 
which tends to the North pole of the Earth, and the 
negative pole is that which is attracted to the South pole of 
the Earth. Hence regarding the Earth as a magnet, its 
North pole must be negative and its South pole positive. 
If the magnetic energies move along the surface of the 
Earth from North to South, then the magnetic energies of 
the needle which points to the North must move along the 
surface of the magnet from its negative to its positive pole ; 
for it is necessary, as I have explained, for the magnetic 
energies or currents to move in opposite directions to pro- 
duce attraction. The magnetism of the Earth has been 
supposed to be due to electric currents generated by the 
unequal heating of the Earth by the rays of the Sun and 
passing along the surface of the Earth from East to West. 
Now if we suppose the magnetic currents to move along 
the Earth's surface from North to South, we readily under- 
stand how the molecules on the Earth's surface are rotated 
by the electric currents from East to West in order to pro- 
duce magnetism. We may illustrate the motions of these 
molecules by imagining them to be strung on a wire 
stretched from North to South and rotating in the same 
direction as the Earth on its axis, or against the motion of 



88 A THEOEY OF GRAVITATION, 

the Sun. Then let the north end of the wh'e be imagined to 
be carrit^d around to .the East and the South end to the 
West. It is plain that this motion of the molecules wonld 
tend to drive their caloric atmospheres in a southerly 
direction. 

Now if we suppose a magnet or solenoid to be directed by 
the Earth's magnetism with its north or positive pole to the 
north pole of the earth its magnetic currents must move 
opposite to those of the Earth. Therefore the molecules at 
the top of the solenoid move in an opposite direction to those 
npon the surfiice of the earth, and the molecules at the bot- 
tom of the solenoid move in the same direction as those of 
the Earth. Now if we suppose that an electric current always 
polarizes the molecules of the circuit in the same direction 
from right to left as the thermo-electric currents flowing 
through the Earth were supposed to do, then we must sup- 
pose that the electric currents, which produce the magnet- 
ism of the solenoid directed as above, must move around 
the solenoid from right to left over it and in the opposite 
direction under it ; so that over those parts of the Earth 
and solenoid Avhich are adjacent the currents of electricity 
move in the same direction. But it w^ould make no differ- 
ence at which end of the solenoid the electric current enters, 
provided it flows across the solenoid in the same direction. 
But to make the current flow in the tvv^o cases in the same 
direction across the solenoid the wire of the solenoid would 
have to be coiled in opposite directions. If a current of 
electricity moved around the coil as the hands of a watch, 
the face of the watch will represent the south pole and the 
back of the watch the north pole of the solenoid or magnet, 
whether the current commence at the back or enter from 
the front. 

In all these cases the magnet acts as the solenoid, and 
comports with the hypothesis that there is a sameness in 



HEAT AND ELECTRICITY. 89 

their molecular structure. Magnets and solenoids differ, 
however, in one remarkable respect, to which I will now 
advert. The coil induces a magnetism in a bar of soft iron, 
placed in the coil, unlike that magnetism induced by a hol- 
low magnet. The bar serves only to strengthen the magne- 
tism of the coil, which becomes saturated when it has reached 
a certain point. But if a bar of soft iron is placed within 
a hollow magnet, the north pole of the magnet will induce 
a south pole in the bar, and the south pole of the magnet 
will induce a north pole in the bar. Thus the coil and the 
hollow magnet produce opposite results. If, instead of a 
bar of soft iron, a bar of steel be inserted in the coil, it is 
found that the magnetization can go on only to a certain 
point, and that the steel is sooner saturated than the soft 
iron, but retains its magnetism longer. Again there are 
some bodies which instead of being attracted by the poles of 
a magnet, are repelled and tend to place themselves across it 
at right angles to its axis. All these fac!s tend to show 
that, while the internal structure of magnets agree in cer- 
tain respects, there are, on the other hand, certain other 
respects in which they differ not only from solenoids but 
disagree among themselves. 

In order to explain the difference above stated in the 
actions of solenoids and magnets, it has been said that a 
hollow magnet acts not as a single solenoid, but as if it were 
composed of an immense number of little solenoids arranged 
together side by side. If it be a bar of soft iron, which is 
magnetized, the little solenoids are placed in parallelism by 
the electric current, but move out of parallelism when the 
current ceases. A bar of hard iron or steel contains not so 
many of these solenoids as a bar of soft iron of the same 
weight, nor are they so free to move ; but after they have 
been arranged in parallel rows by the action of magnetic 
energies, owing to the entanglement of other matter with 

8* 



90 A THEORY OF GRAVITATION, 

these solenoids, they retain their positions longer in the steel, 
than in the soft iron. But the fact that bodies become satu- 
rated with magnetism, is a proof, that magnetism is due to 
molecular forces. For after all the solenoids, which a bar of 
soft iron or a bar of steel contains, have been arranged in 
parallelism, the bar of iron or steel cannot be made more 
magnetic by increasing the current of electricity in the coil. 
The Earth, Vvhich is considered to be a vast magnet, 
differs from the steel magnet as the steel from the bar of 
soft iron; that is to say, it contains not so many solenoids in 
proportion to its magnitude. The Earth is not a permanent 
magnet, nor is it saturated with magnetism, but it is subject 
to magnotic storms, as if the coil or solenoid, as it were, 
which engirds it, were sometimes twisted out of position, so 
that the electric currents, whose general direction is from 
east to west, are shifted from their course and vary in direc- 
tion as well as in strength and intensity. The varying tem- 
perature of the Earth's surface is one of the causes, which 
affect the passage of these currents. For the magnetism of 
the Earth is found to undergo annual variations from winter 
to summer and from summer to winter again, and in like 
manner with the fluctuations of temperature it is subject to 
daily variations. That these currents should circulate around 
the Earth, instead of penetrating and passing through it, 
may be due to the fact, that the Earth increases in tempera- 
ture as we proceed downwards. It is even supposed by some, 
that the inhabited Earth is but a comparatively thin crust 
resting upon a molten and liquid mass. Hence the outer 
coating of the Earth may be in the nature of a circuit, insu- 
lated by the atmosphere on the one side and by the intensely 
heated substances of the interior on the other side. So that 
be the cause what it may, by which electric currents are 
generated in the Earth, they seek the best conductors and 
flow around it, instead of penetrating to its interior, or flying 
off into the regions of space. 



HEAT AND ELECTRICITY. 91 



CHAPTER VIT. 

ON THE GENERAL DISTURBANCE OF ELECTRICAL EQUILIBRIUM BY 
THE MOVEMENTS OF THE HEAVENLY BODIES. 

According to the double ether hypothesis, all space is 
conceived to be filled with two fluids, ether and caloric, 
which mix with each other and vary in density with the mass 
and distance of bodies which they surround. The union 
of these and their passage in the same direction constitutes 
fluid heat, and their separation and passage in opposite 
directions produce electrical phenomena. I have explained 
already, how the movements of atoms and molecules afiect 
the distribution of these fluids both in regard to heat and 
electricity. I now propose to explain the eff'ects produced 
upon them by the movements of the Earth and celestial 
bodies, so as to account for the magnetism of the Earth, the 
luminosity of the Sun and Stars and the singular disturb- 
ance of the matter of Comets, as they approach or recede 
from the Sun. 

First let us inquire into the nature of the source of the 
Earth's magnetism. This is sometimes supposed to be due 
to electric currents generated by the unequal heating of the 
Earth by the rays of the Sun and passing along the surface 
of the Earth from East to West. It is plain, that this 
hypothesis cannot apply to the magnetism of the Sun, if the 
Sun, as some suppose, be a magnet. The hypothesis 
which I propose, applies to all the heavenly bodies, which 
have atmospheres like the Earth and motions like it upon 
their axis and in elliptical orbits. For the present I will 
consider only the effect of the Earth's motions around the 
Sun, and will explain how this motion disturbs the equilib- 



92 A THEORY OF GRAVITATION, 

rium between the ether and caloric, and how the flow of 
these fluids to restore equilibrium produces the magnetism 
of the Earth. 

According to the hypothesis of gravity, which I have 
presented in the aforegoing pages, I have represented it to be 
the property of caloric, owing to the pressure of ether, to 
be densest at the center of a gravitating body and to decrease 
outwardly in density, in the manner of the atmosphere, 
which surrounds the Earth. The movement of the Earth 
through space, therefore, would have a tendency to carry it 
away from that part where the caloric is densest, or out of 
the caloric globe ; and we must see, that the pressure of the 
ether would cause the caloric to follow the Earth. The 
Earth and caloric would not move in virtue of the same 
principle. The force which moves the Earth is the property 
of inertia in its mass; the force, which moves the caloric 
globe, after the Earth, would be the extraneous pressure of 
ether. They would not move together. Hence, on account 
of the motion, which tends to carry the Earth away from 
the caloric, a certain part of the Earth would always be 
positive or have a superabundance of caloric, or positive 
electricity, and another part would be negative. The place 
from which the Earth is moving must be positive, and the 
place to which it is moving, negative. We may say, there- 
fore, that the Earth's surface is at a difierent potential in one 
part from what it is in another ; and that it is at a higher 
potential on that side from which it moves, than on the side 
opposite. 

If the orbital motion of the Earth were always uniform, 
and the Earth had no axial revolution, the difierence of 
potential produced by its projection could not generate cur- 
rents of electricity ; but the same relation would exist between 
the positive and negative points of the Earth, as is sometimes 
induced by a constant and uniform current of electricity in 



HEAT AND ELECTRICITY. 93 

the two opposite points of a broken circuit. The analogy 
goes farther. As long as the inducing current remains con- 
stant and uniform, the difference of potential in the oppo- 
site points of the broken circuit, remains constant and no 
current is induced; but if the strength of the inducing 
current increases or diminishes, the difference of potential 
increases or diminishes in proportion and a current of elec- 
tricity is induced. When the inducing current increases, 
the induced carrent flows from the negative to the positive 
point in the broken circuit, and in the reverse direction, 
when the inducing current is diminished. So it would be 
with the positive and negative points above referred to, in 
the surface of the Earth, supposing it to have no motion on 
its axis, but only a rectilineal projection, or the motion 
in its orbit. We will say that this projection is from West 
to East ; we may, therefore, regard the western extremity of 
the Earth as the positive point and the eastern extremity as 
the negative point. The Earth's motion in its orbit is not 
uniform ; but varies with every day in the year. During one 
half of the year, as it approaches its perihelion, its motion 
is accelerated ; during the other half its motion is retarded. 
Now let us inquire what would be the effect of the Earth's 
axial or diurnal motion upon its electrical potential. 

We know that the Earth moves on its axis from West to 
East, which causes the Sun to appear to move from East to 
West. If we suppose the alphabet A, B, C, D, etc., to repre- 
sent the motion of the Earth on its axis from West to East, 
then the Sun will apparently move against the alphabet, or 
in the direction D, C, B, A ; and we may now demonstrate, 
that a current of positive electricity would flow around the 
Earth in the same direction as the apparent motion of the 
Sun. We must bear in mind, that although the ether or 
negative electricity flows with the utmost freedom through 
the pores of ponderable matter, caloric or positive electricity 



94 A THEORY OF GRAVITATION, 

does not, and the amount of resistance, which it encounters 
in its passage, is what constitutes or distinguishes a good or 
bad conductor. Hence the surface of the Earth being 
brought by its axial rotation to that point, where the poten- 
tial is highest, would collect positive electricity, and would 
carry it around in the direction A, B, C, D ; until the tension 
of the electricity at C or D would be sufficient to overcome 
the resistance of the conductor and cause the current to 
flow from C or D to A, or against the alphabet. On the 
contrary, the opposite point on the Eartli's surface charged 
with negative electricity and moving in the direction A, B, 
C, D would attract the opposite electricity. Hence there 
would be a continuous flow of electricity from East to West. 

The resistance referred to above might be greater or less 
according to the temperature of the conductor. Hence 
fluctuations of temperature may have much to do in occa- 
sioning those electrical storms, which sometimes result from 
difference of potential of some localities on the Earth's sur- 
face and affect telegraphic communication. A higher tem- 
perature would increase the resistance of the solid substances 
of the Earth, and would diminish that of the atmosphere. 
Hence upon the temperature might depend, whether the 
surface of the Earth or the atmosphere would carry the 
electricity back to C or to D. If the surface of the Earth, 
heated, would carry the fluid to D ; when cooled it would 
carry the electric fluid only to C. The point on the Earth's 
surface, therefore, corresponding to D would have a higher 
potential than the point C, and being connected by a tele- 
graph wire or any other good conductor a current of electri- 
city would flow between them. 

These currents flowing along the Earth's surface from 
East to West would produce magnetism in the same manner 
as the thermo-electric currents generated by the heat of the 
San. They would flow chiefly through the Earth's surface 



HEAT AND ELECTRICITY. 95 

and not through the atmosphere. For without regard to 
temperature, some bodies admit the passage of caloric more 
readily than others ; hence good conductors in passing the 
positive pomt, would collect more, but retain less positive 
electricity than more imperfect conductors. The atmosphere 
for this reason would collect less caloric than the Earth at 
the positive point, but it would retain it longer. Hence the 
flow of current through the atmosphere might not be suffi- 
cient to afiect the Earth's magnetism to a very great extent. 
I have thus far considered only the effect of the pro- 
jection of the Earth upon its potential, without taking into 
consideration the existence and action of other bodies as the 
Sun and Moon. The gravity of these bodies is perhaps a 
far more potent agent in producing the points of high and 
low potential and destroying electrical equilibrium of the 
Earth's surface, than the projection of the Earth. In what- 
ever place the caloric would be densest would be the point 
of high potential, and where the caloric is least dense would 
be the point of low potential. Now according to the theory 
which 1 have proposed for the explanation of the gravi- 
tating force, the caloric is supposed to decrease in density 
as we proceed from dense bodies outwardly, and when two 
bodies gravitate to one another the caloric grows in density 
between them. Hence the Earth's high potential point 
would be on the side next to the Sun or Moon, as on this 
side the caloric is densest, and its low potential point 
would be the side opposite to the Sun or Moon. I suppose 
the theory of gravity, which I have proposed in the pre- 
ceding pages, to be w^ell enough understood to make this 
clear. Hence the Earth might have two points of high 
poteutial on its surface and two points of low potential, 
according to the positions of the Sun and Moon. For 
each of thess bodies would have a tendency to raise a point 
of high potential and a point of low potential ; but when 



96 A THEORY OF GRAVITATION, 

they happen to be on the same side of the Earth the two 
points of high potential would coincide, and be on the side 
of the Earth next to these bodies, and the two points of low 
potential would likewise coincide and be on the opposite 
side of the Earth. The effect however, in producing 
electric currents would probably be the same, whether 
there be one or two points of high or low potential; at least 
so far as their direction is concerned, this being due to the 
rotation of the Earth on its axis. The Earth's projection 
or the Sun's gravitation disturbs the electrical equilibrium 
on the Earth's surface, and its revolution on its axis pro- 
duces the flow of electricity from East to West. I have said, 
that the difference of potential between the positive and 
negative points would be increased with an increase of the 
Earth's projection, and vice versa, I was then considering 
the effect of this motion upon the potentials, independ- 
ently of the Sun's attraction. Gravity would have the 
effect of reversing this result; for when the Earth moves 
away from the Sun, its motion and gravity act together in 
raising the Earth's potential on the side next to the Sun; 
but when the Earth approaches the Sun, the Earth's 
motion and gravity counteract each other by raising poten- 
tial on opposite sides. Hence the strength of the Earth's 
currents and the intensity of its magnetism, depending on a 
varying potential, must be greatest during the passage of 
our planet from its winter to its summer solstice and least 
upon its return. 

So far, I have considered only that cause which affects the 
electrical equilibrium of the Earth's surface and causes one 
locality to be at a higher potential than another. I will 
now consider another effect of the Earth's motion of no less 
importance perhaps than that which I have considered in 
the preceding pages. It is that effect of its motions, which 
causes it to be at one time of a higher potential, than the 



HEAT AND ELECTRICITY. 97 

regions of space surrounding it, and at another time at a 
lower potential. I wish to show, why it is, that the upper 
regions of the Earth's atmosphere are sometimes positive 
and sometimes negative, and at what seasons we should 
expect this difference of electrical state to occur. For 
besides the electrical disturbance, which takes place upon 
the surface of the Earth and produces magnetism, there is 
an electrical disturbance produced by a similar cause in 
the upper regions of the Earth's atmosphere, which probably 
gives rise to the phenomena of the aurora borealis. This 
disturbance is due in part to the Earth's motions and partly 
to the non-conducting properties of the atmosphere. For if 
caloric passed as readily through all bodies as ether and 
through all bodies alike, no electrical disturbance would 
ever take place. What I mean by an electrical disturbance 
is a disturbance of that condition of density, which the 
caloric is supposed to assume under the pressure of ether 
around all bodies; for the pressure of the ether causes the 
caloric to assume a certain condition, and if this condition 
is disturbed or altered by any foreign cause, as the motions 
or positions of the heavenly bodies, it will return to its 
normal condition again, as soon as the resistance is over- 
come. The condition of the caloric or positive electricity 
around the Earth Avould vary with its distance from the 
Sun. For the density of the caloric Avould diminish 
around the Earth, as the Earth approached the Sun, and it 
would increase as the Earth receded again. (For the gravity 
of bodies to the Earth is diminished by the attraction of 
the Sun ; on this principle the rise and fall of the tides are 
explained.) But for a given distance, its density would be 
always the same. This condition of the caloric I have 
explained under the head of gravity. I will now explain 
how the motions of the Earth may disturb it. 

First, then, let us suppose, that the caloric is in that con- 



98 A THEORY OF GRAVITATION, 

clition of density around the Earth, which it would assume 
if no change took place in the Earth's distance from the 
Sun. We will then say, that its caloric atmosphere is in 
electrical equilibrium. This would occur if the Earth's 
orbit were a circle. But none of the planets move in per- 
fect circles; and the comets^in which the electrical disturb- 
ance would be greatest, move around the Sun in orbits, 
which are very eccentric. When the earth moves from its 
perihelion to its aphelion, the density of the caloric has a 
tendency to increase around the Earth, and therefore the 
caloric passes to the Earth from the regions of space, or we 
will say from the upper regions of the air. But the flow of 
the caloric to the Earth will be resisted by the non-conduct- 
ing properties of the aerial atmosphere surrounding it. 
The atmosphere, or upper regions, will then be positive and 
the Earth negative during the season of the year when the 
Earth passes from its winter to its summer solstice. A vast 
amount of electricity might thus accumulate in the upper 
regions, w^here the air is very attenuate and a better con- 
ductor, than it is in the lower regions near the Earth's sur- 
face. But when the Earth leaves its aphelion and approaches 
the Sun, its caloric atmosphere will have a tendency to de- 
crease in density, until the Earth arrives at its perihelion. 
The Earth is now positive and space negative, and the cur- 
rent has a tendency to flow from the positive to the negative 
body. The upper regions of the air being a good conductor 
are soon discharged of their positive electricity; but the 
lower regions of the atmosphere, where the air is dense, 
resists the flow of electricity from the Earth. The electrical 
conditions of the Earth and its aerial atmosphere therefore 
are reversed at the opposite seasons of the year, when the 
Earth approaches and recedes from the Sun. The passage 
of electricity due to this change of electrical condition here 
pointed out may produce some of those luminous phenomena, 



HEAT AND ELECTRICITY. 99 

known as the aurora borealis, in the Earth's atmosphere, as 
well as the luminous clouds of some other planets, but 
especially that brilliant appearance of comets. 

Now the electrical phenomena, which are produced, must 
depend on two causes; first, the tension of the electromotive 
force, which is greater or less according to the eccentricity 
of the planet's orbit ; second, the resistance of the air, w^hich 
depends upon its magnitude and density. We should, there- 
fore, expect to find a more brilliant electrical display in the 
case of a comet, than in the case of a planet. An orbit 
nearly circular and an extremely small and rare atmosphere 
may be the cause of the faint luminosity of the planet Jupi- 
ter, notwithstanding the greatness of his mass and motions; 
for we know, that the voltaic arc is much more brilliant, 
when the current is passed through air of ordinary density, 
than v/hen passed through a partial vacuum. On the other 
hand, the comets are self-luminous bodies, although ex- 
tremely small. But their mot'ons are vast; their atmos- 
pheres are extensive; and their orbits are very eccentric. 
All these properties of comets here enumerated tend to pro- 
duce change in their electrical conditions, like those which 
I explained as produced in the Earth by its varying motion 
and elliptic orbit. 

Let us consider again Avhat this change is, and I think we 
will be able to form some idea of the cause of the comet's 
luminosity, as well as of the repulsion of luminous matter 
from the body of the comet as it approaches the Sun, and 
we will be able to see, too, why the luminous matter is re- 
pelled from the comet in a particular direction, that oppo- 
site the Sun. To discuss this change it is necessary to 
understand the nature of gravity, and the relations of ether 
and caloric. A comet may be nothing more than a body of 
vapor; but let us take for example such a one as has a solid 
body for a nucleus. 



100 A THEORY OF GEAYITATION, 

Now we know, that as any body, whether it be a planet 
or a comet, approaches the Sun, its own gravitation to the 
Sun increases; but the gravitation to it of bodies on its sur- 
face is diminished. The atmosphere of a comet or any object 
floating in its atmosphere, for example, is attracted more 
strongly by the comet as it recedes from the Sun, and the 
attraction is diminished as the comet approaches. Hence 
from what I have already said on the relations of ether and 
caloric in explaining the subject of gravity, we must infer 
that the caloric atmosphere of the comet has a tendency to 
become denser as it recedes from the Sun, and to become 
rarer as it comes nearer to that body. For the Sun dimin- 
ishes the attraction of the comet for its atmosphere or for 
objects floating in its atmosphere by exerting an influence in 
rarefying the caloric around the comet. Hence the comet 
has a tendency to absorb positive electricity and to discharge 
negative electricity as it recedes from the Sun; but as it 
approaches the Sun, it has a tendency to part with caloric 
or positive electricity. In other words, as the comet ap- 
proaches the Sun, it becomes more and more positive, — its 
potential is raised. 

Now negative electricity or ether, on account of its ex- 
treme rarity, passes without resistance ; but the atmosphere 
of the comet may be supposed to be of a gaseous nature, 
and, like the aerial atmosphere of the Earth, a non-conduc- 
tor of positive electricity. AVe may further suppose, that 
the comet's atmosphere, like the Earth's, improves in con- 
ductivity as its temperature is raised. Now the comet ap- 
proaches the Sun, carrying with it positive electricity, and 
its potential grows up more and more as it approaches; 
until finally bursting through or overcoming the resistance 
of the non-conducting atmosphere, the electric fluid carries 
the atmosphere with it, into the regions of space opposite 
the Sun, which are negative. It first flies out into the 



HEAT AND ELECTRICITY. 101 

direction of the Sun, because this side of the comet's atmos- 
phere is heated and rendered a better conductor than the 
opposite side; but it no sooner has escaped to the outside of 
the comet's atmosphere and beyond its resistance, than its 
path is changed into the direction opposite the Sun and 
takes the form of a hollow cone as it is turned back over 
the comet. This constitutes the comet's tail. 

The motion of the Sun around the center of the Universe 
or of some smaller system, may produce effects like those 
ascribed to the motion of the planets and comets around the 
Sun. It may render him magnetic by generating electric 
currents in his surface, and it may render him luminous by 
generating electric currents in the upper regions of his 
atmosphere. Thus it may be supposed, that the Sun's mo- 
tion and gravity to the center of the Universe is the fuel, 
which feeds his fires, and this fuel will continue to burn 
without diminution, until the planets shall all have sunk 
into the Sun and become extinct, and finally the Sun him- 
self shall sink into the center of the Universe and become a 
motionless mass, unless regenerated into new life by the 
quickening power of the Almighty. 

There is a hypothesis which explains the origin of the 
heat and light which we receive from the Sun, as due to the 
same cause as the interior heat of the Earth. It is supposed, 
that the entire solar system once existed in a single mass, 
and that by virtue of intense heat this mass was in the con- 
dition of vapor. For matter contains more heat in the state 
of vapor, than in the liquid state, and more in the liquid, 
than in the solid. In passing, therefore, from the first state 
to the last, it throws off heat. It is supposed that by the 
contraction of the mass above mentioned, the planets were 
separated one by one in the order of their distance at the 
present time from the Sun, first Neptune, tnen Uranus, and 
last Mercury. As the original mass contracted, its motion 



102 A THEORY OF GRAVITATION 



was quickened and gave to each new planet as it sprang 
from the original a greater velocity in its orbit, than the one 
which preceded it. The planets in turn undergo a contrac- 
tion like that of the original mass. Finally they pass from 
the state of vapor to a state of liquid, and from liquid into 
solid masses, solidifying first at their surfaces, and at the 
same time they evolve an enormous amount of heat. This 
is known as the nebular hypothesis. It both presents us 
with an account of the origin of the Universe, too beautiful 
not to be true, and it is one attempt to explain the source of 
the Sun's heat as well as the interior heat of the Earth. 

If this hypothesis be extended so as to apply to the whole 
Universe, to explain its separation into starry clusters and 
solar systems and the motions of all these among them- 
selves, some around others and all around a common center, 
it may be asked, what became of the enormous amount of 
heat, which was set free, when the original mass of vapor 
was cooled down? It is plain, that we cannot answer this 
question upon the assumption, that heat is purely force or 
the motion of atoms and molecules, if we hold to the doc- 
trine of conservation. For if the heat of the Universe were 
sufficient at any time to support it in the state of vapor, and 
the conservation doctrine hold true, it would be sufficient to 
support it in a state of vapor for all time. For although we 
may say, that the heat, which sustained the solar system in 
a state of vapor, passed off into space, meaning thereby the 
matter, which occupies the space of the Universe, yet we 
could not affirm, that the heat, which sustained the Universe 
in a state of vapor, had passed off into space, without admit- 
ting, that it is entirely lost or annihilated. For matter and 
force are inseparable. It appears to me, therefore, that the 
nebular hypothesis is irreconcilable with that view of heat, 
which altogether excludes a material theory and makes it 
consist entirely in motion. It may be said, that heat is con- 



HEAT AND ELECTRICITY. 103 

verted into other forces. But into what other force could 
such a vast amount of heat be converted ? But if we take 
the view, which I have explained upon the basis of the 
double-ether hypothesis, that heat consists not of force only 
but also of fluid, we may reconcile the nebular hypothesis 
with the principle of conservation by the assumption, that 
the heat evolved during the contraction of the nebular 
masses consists of fluid heat, and that the cooling process 
consists in the separation of this fluid from the ponderable 
matter which composes those masses. 

There is another hypothesis of the source of the Sun's 
heat and light, which ascribes it to the incessant impact of 
falling bodies, which are drawn to the Sun by the force of 
gravity and the resistance of the interstellar medium. The 
occasional fall of a meteoric stone to the Earth and the 
shortening of the periods of the comets are phenomena, 
which appear to give some support to this hypothesis and 
have caused it to attract considerable attention. 

There are facts, however, which do not sustain either of 
these two last-mentioned hypotheses concerning the source 
of solar heat, but seem to indicate that the heat and light of 
the Sun are related to the causes of the Earth's magnetism 
and are due to electric currents in his atmosphere. The 
magnetic needle has been observed to be affected apparently 
by the occurrence and disappearance of the Sun's spots. 
Moreover, the most brilliant part of the Sun's luminous 
atmosphere, like the aurora in the Earth's atmosphere, is in 
the neighborhood of his poles. Whereas we should think 
that the impact of meteors should take place chiefly about 
his equatorial regions; and we should think that the solid 
part of the Sun would be rendered thus far hotter than his 
atmosphere; and if hotter, more luminous. For we know, 
that flame owes its luminosity to the heated solid particles, 
which it contains, and that the solid particles are rendered 



104 A THEORY OF GRAVITATION, ETC. 

luminous at a much lower temperature, than the gas. The 
nebular hypothesis, therefore, and the impact theory of 
meteors do not explain these phenomena of the Sun's lumi- 
nosity in conformity with our ideas of illumination, accord- 
ing to which solid substances produce a more brilliant 
incandescence, than those in the form of gas, except in the 
passage of electricity through attenuated air, when no com- 
bustion takes place. Analogy would thus lead us to con- 
clude, that the Sun's heat is generated in his atmosphere 
and not upon his solid crust ; and that the cause is related 
to the cause, which produces the aurora borealis, the lumi- 
nous clouds of Jupiter and the brilliant light of comets, as 
well as the magnetism of the Earth. 

Thus gravity, heat and electricity appear to be co-exten- 
sive forces, residing in all space and exerted upon matter 
through the agency of two ethers. When the gravitating 
force is resisted by the motion of the heavenly bodies, the 
equilibrium of the fluids is destroyed and electricity is ex- 
cited; and electric currents thus produced are the source of 
heat and light. 



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